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PROGRAM:

NAME


S-nail [v14.8.6] — send and receive Internet mail

SYNOPSIS


s-nail -h | --help
s-nail [-BDdEFintv~] [-A account] [-a attachment] [-b bcc-addr] [-c cc-addr] [-q quote-file]
[-r from-addr] [-S variable[=value]] [-s subject] [-X cmd] [-.] to-addr ... [--
mta-option ...]
s-nail [-BDdEeHiNnRv~#] [-A account] [-L spec-list] [-r from-addr] [-S variable[=value]]
[-X cmd] -f [file] [-- mta-option ...]
s-nail [-BDdEeHiNnRv~#] [-A account] [-L spec-list] [-r from-addr] [-S variable[=value]]
[-u user] [-X cmd] [-- mta-option ...]

DESCRIPTION


Compatibility note: S-nail and part of its configuration syntax will change in v15.0.
Until then there will exist a partial but growing number of backward and forward
compatibility configuration options. To choose the new syntax and behaviour already
today, the binary option v15-compat must be set. The manual will refer to it via
[v15-compat] and [no v15-compat] as necessary. Commands and variables which will
vanish in v15.0 are marked [Obsolete].

S-nail is a mail processing system with a command syntax reminiscent of ed(1) with lines
replaced by messages. It is intended to provide the functionality of the POSIX mailx(1)
command and offers (mostly optional) extensions for line editing, IDNA, MIME, S/MIME, SMTP
and POP3 (and IMAP). It is usable as a mail batch language.

Options
-A account Executes an account command (see below) for account after the startup files have
been read.

-a file Attach the given file to the message. The same filename conventions as
described in the section COMMANDS apply: shell word expansion is restricted to
the tilde ‘~’ and variables. Shall file not be accessible but contain a ‘=’
character, then anything after the ‘=’ is assumed to specify the input character
set and anything before ‘=’ the filename: this is the only option to specify the
input character set (and don't perform any character set conversion) for text
attachments from the command line, not using the ~@ tilde escape command.

-B Make standard input and standard output line-buffered.

-b address Send blind carbon copies to the given list of addresses. Sending mail below
goes into more detail on that.

-c address Send carbon copies to the given list of addresses.

-D [Option] Set the disconnected variable.

-d Set the debug variable, which enables debug messages and disables message
delivery.

-E Set the skipemptybody variable and thus discard messages with an empty message
part body. This is useful for sending messages from scripts.

-e Just check if mail is present in the system mailbox. If yes, return an exit
status of zero, a non-zero value otherwise.

-F Save the message to send in a file named after the local part of the first
recipient's address (instead of in record).

-f [file] Read in the contents of the user's MBOX (or the specified file) for processing;
when S-nail is quit, it writes undeleted messages back to this file (but be
aware of the hold option). Some special conventions are recognized for the
string file which are documented for the file command below. Note that file is
not a direct argument to the flag -f, but is instead taken from the command line
after option processing has been completed. In order to use a file that starts
with a hyphen, prefix it with a (relative) path, as in ‘./-hyphenbox.mbox’.

-H Print a header summary of all messages and exit. A configurable summary view is
available via the -L option.

-h Print a short usage summary. Because of widespread use a --help argument will
have the same effect.

-i Set the ignore variable to ignore tty interrupt signals.

-L spec-list
Print a header summary of only those messages that match the given spec-list,
then exit. See the section Specifying messages for the format of spec-list. If
the -H option has been given in addition no header summary is produced, but
S-nail will instead indicate via its exit status wether spec-list matched any
messages (‘0’) or not (‘1’); note that any verbose output is suppressed in this
mode and must instead be enabled explicitly (e.g., by using the option -v).

-N Unset the header variable and thus inhibit initial display of message headers
when reading mail or editing a mail folder.

-n Inhibits reading s-nail.rc upon startup. This option should be activated for
S-nail scripts that are invoked on more than one machine, because the contents
of that file may differ between them. (The same behaviour can be achieved by
setting the NAIL_NO_SYSTEM_RC environment variable.)

-q file Start the message with the contents of the specified file. May be given in send
mode only.

-R Any folder opened will be in read-only mode.

-r address If address is a valid address then it specifies the envelope sender address to
be passed to the MTA as ‘-f address’ when a message is send. Shall address
include a user name, comments etc., then the components will be separated and
the name part will be passed to the MTA individually via ‘-F name’. The given
address will also be assigned to the from variable, just as if additionally
‘-Sfrom=address’ had been specified (therefore affecting SMTP data transfer,
too).

If instead an empty string is passed as address then the content of the variable
from will be evaluated and used for this purpose whenever the MTA is contacted.
Note that S-nail by default, without -r that is, neither passes ‘-f’ nor ‘-F’
flags to the MTA by itself.

-S variable[=value]
Sets the internal option variable and, in case of a value option, assigns value
to it. Even though options set via -S may be overwritten from within resource
files, the command line setting will be reestablished after all resource files
have been loaded.

-s subject Specify the subject of the to-be-sent message.

-t The message to be sent is expected to contain a message header with ‘To:’,
‘Cc:’, or ‘Bcc:’ fields giving its recipients, which will be added to those
given on the command line. If a message subject is specified via ‘Subject:’
then it'll be used in favour of one given on the command line.

Also understood are ‘Reply-To:’ (possibly overriding replyto), ‘Sender:’ (p. o.
sender), ‘Organization:’ (p. o. ORGANIZATION). Note you can also specify
‘From:’, possibly overriding from and the envelope address possibly specified
with the option -r!

The following, which are normally created automatically based upon the message
context, can also be specified: ‘Message-ID:’, ‘In-Reply-To:’, ‘References:’ and
‘Mail-Followup-To:’ (special address massage will however still occur for the
latter).

-u user Read the system mailbox of user (appropriate privileges presumed), and “assume
to be” user in some aspects, e.g. in respect to file–expansions of ‘%’ etc.;
also see USER.

-V Print S-nail's version and exit.

-v Setting the verbose option causes some verbosity (like printing of certificate
chains). Using it twice increases the level of verbosity.

-X cmd Add the given cmd to the list of commands to be executed before normal operation
starts. Correlates with -# and batch-exit-on-error; the only possibility to
execute commands in non-interactive mode when reading startup files is actively
prohibited.

-~ Enable TILDE ESCAPES even if not in interactive mode.

-# This sets several options to prepare S-nail for working in (most likely non-
interactive) batch mode: dot, emptystart, noheader, quiet, sendwait, as well as
MBOX and folder (both to /dev/null). It also enables processing of TILDE
ESCAPES. E.g., the following should send an email message to “bob”:

$ LC_ALL=C printf 'm bob\n~s ubject\nText\n.\nx\n' | \
LC_ALL=C MAILRC=/dev/null s-nail -n -# -Snosave

-. This flag forces termination of option processing in order to prevent “option
injection” (attacks). It also forcefully puts S-nail into send mode, see
Sending mail.

In the above list of supported command line options, -D, -d, -E, -i, -N and -v are
implemented by means of setting the respective option, as via -S. [mta-option ...]
arguments that are given at the end of the command line after a ‘--’ separator will be
passed through to the mail-transfer-agent (MTA) and persist for an entire (interactive)
session – if the setting of expandargv allows their recognition; MTA arguments can also be
specified in the variable sendmail-arguments; find MTA interaction described in more detail
in the documentation of sendmail. MTA arguments are ignored when mail is send via SMTP data
transfer.

A starter
S-nail is a direct descendant of the BSD Mail program that was introduced in 1978 (itself
superceeding the simpler UNIX mail program) and used to introduce itself (in the Mail
reference manual) as follows:

Mail provides a simple and friendly environment for sending and receiving mail. It
divides incoming mail into its constituent messages and allows the user to deal with
them in any order. In addition, it provides a set of ed(1)-like commands for
manipulating messages and sending mail. Mail offers the user simple editing
capabilities to ease the composition of outgoing messages, as well as providing the
ability to define and send to names which address groups of users.

S-nail is thus the user side of the Unix mail system, whereas the system side (mail-
transfer-agent, MTA) was traditionally taken by sendmail(8); today postfix(1) or exim(8) are
often used for this purpose instead. If the [Option]al SMTP feature has been built into
S-nail then the system side is not a mandatory precondition for mail delivery.

Because S-nail strives for compliance with POSIX mailx(1) it is likely that some
configuration settings have to be adjusted before using it is a smooth experience. The
default global s-nail.rc file already bends those standard settings a bit towards more user
friendliness and safety, e.g., it sets the hold and keepsave options in order to suppress
the automatic moving of messages to MBOX that would otherwise occur (see Message states) and
keep to not remove empty files in order not to mangle file permissions when files eventually
get recreated. It does not set the folder option so that by default file grouping (via the
‘+’ prefix as documented also for file) is not enabled. The section EXAMPLES contains some
further suggestions.

Sending mail
To send a message to one or more people, using a local mail-transfer-agent (MTA; the
executable path can be set via sendmail) or the [Option]al builtin SMTP (set and see the
variable smtp) transport to actually deliver the generated mail message, S-nail can be
invoked with arguments which are the names of people to whom the mail will be sent:

$ s-nail -s Subject -a attachm.ent bill@host1 'Bob <bob@host2>'
# But... try it in an isolated dry-run mode first
$ LC_ALL=C MAILRC=/dev/null \
s-nail -n -d -vv -Sfrom="me <he@re>" \
-s Subject -. "(Lovely) Bob <bob@host2>"

The user is then expected to type in the message contents. In this compose mode S-nail
treats lines beginning with the character ‘~’ special – these are so-called TILDE ESCAPES
which can be used to read in files, process shell commands, add and edit attachments and
more; e.g., the tilde escape ‘~e’ will start the text editor to revise the message in it's
current state, ‘~h’ allows editing of the message recipients and ‘~?’ gives an overview of
available tilde escapes. Typing control-D ‘^D’ at the beginning of an empty line leaves
compose mode and causes the message to be send, whereas typing control-C ‘^C’ twice will
abort the current letter (saving its contents in the file denoted by DEAD unless nosave is
set.)

A number of options can be used to alter default behavior; e.g., setting (also via -S)
editalong will automatically startup a text editor when compose mode is entered, askcc will
cause the user to be prompted actively for carbon-copy recipients and the dot option will
allow leaving compose mode by writing a line consisting solely of a dot (‘.’).

Very important, though, is to define which Character sets may be used when sending messages,
usually by setting the option sendcharsets accordingly, having read the section The
mime.types files to understand how the MIME-type of outgoing attachments is classified and
the knowledge that messages are sent asynchronously unless sendwait is set: only with it MTA
delivery errors will be recognizable.

Setting from is often necessary (e.g., in conjunction with smtp) or desirable, you may want
to do some dry-run tests before you go. Saving a copy of the sent messages in a record may
also be desirable – as for most mailbox file targets some special conventions are
recognized, see the file command for more on that. The section On URL syntax and credential
lookup will spread some light on the ‘USER@HOST’ variable chains as well as on using URLs
for accessing protocol-specific resources, like smtp, and EXAMPLES contains an example
configuration for sending messages via some of the well-known public mail providers; note it
also gives a compact overview on how to setup a secure SSL/TLS environment.

Message recipients (as specified on the command line or defined in ‘To:’, ‘Cc:’ or ‘Bcc:’)
may not only be email addressees but can also be names of mailboxes and even complete shell
command pipe specifications. Proper quoting may be necessary, e.g., to embed whitespace
characters. (Recall that S-nail deals with mail standards, therefore those define the rules
with which content is interpreted.) If the variable expandaddr is not set then only network
addresses (see mailaddr(7) for a description of mail addresses) and plain user names
(including MTA aliases) may be used, other types will be filtered out, giving a warning
message.

If the variable expandaddr is set then extended recipient addresses will optionally be
accepted: Any name which starts with a vertical bar ‘|’ character specifies a command pipe –
the command string following the ‘|’ is executed and the message is sent to its standard
input; Likewise, any name that starts with the character slash ‘/’ or the character sequence
dot slash ‘./’ is treated as a file, regardless of the remaining content. Any other name
which contains an at sign ‘@’ character is treated as a network address; Any other name
which starts with a plus sign ‘+’ character specifies a mailbox name; Any other name which
contains a slash ‘/’ character but no exclamation mark ‘!’ or percent sign ‘%’ character
before also specifies a mailbox name; What remains is treated as a network address.

$ echo bla | s-nail -Sexpandaddr -s test ./mbox.mbox
$ echo bla | s-nail -Sexpandaddr -s test '|cat >> ./mbox.mbox'
$ echo safe | LC_ALL=C MAILRC=/dev/null \
s-nail -n -Sv15-compat -Ssendwait -Snosave \
-Sexpandaddr=fail,-all,+addr -s test \
-. bob@home.net

It is possible to create personal distribution lists via the alias command, so that, for
instance, the user can send mail to ‘cohorts’ and have it go to a group of people:

alias cohorts bill jkf mark kridle@ucbcory ~/mail/cohorts.mbox

Please note that this mechanism has nothing in common with the system wide aliases that may
be used by the local MTA (mail-transfer-agent), which are subject to the ‘name’ constraint
of expandaddr and are often tracked in a file /etc/aliases (and documented in aliases(5) and
sendmail(1)). Personal aliases will be expanded by S-nail before the message is sent, and
are thus a convenient alternative to specifying each addressee by itself.

To avoid environmental noise scripts should “detach” s-nail from any configuration files and
create a script-local environment, either by pointing the MAILRC variable to a custom
configuration file, or by using the -S command line option to specify options:

$ env LC_ALL=C MAILRC=/dev/null password=NOTSECRET \
s-nail -n -Sv15-compat -Ssendwait -Snosave \
-Sexpandaddr=fail,-all,+addr \
-S 'smtp=smtps://mylogin@some.host:465' -Ssmtp-auth=login \
-S 'from=scriptreply@domain' \
-s 'subject' -a attachment_file \
-. "Recipient 1 <recipient1@domain>" recipient2@domain \
< content_file

Reading mail
When invoked without addressees S-nail enters interactive mode in which mails may be read.
When used like that the user's system mailbox is read in and a one line header of each
message therein is printed. (See the command file for an in-depth description of the
different mailbox types that exist.) Note that if the mailbox is empty S-nail will exit
after printing a message unless the option emptystart is found to be set.

At the prompt the command list will give a listing of all available commands and help will
give a summary of some common ones. If the [Option]al documentation strings are available
one can type ‘?X’ and see the actual expansion of ‘X’ and what it's purpose is, i.e.,
commands can be abbreviated (note that POSIX defines some abbreviations, so that the
alphabetical order of commands doesn't necessarily relate to the abbreviations; it is
possible to define overwrites with the ghost command, however).

Messages are given numbers (starting at 1) which uniquely identify messages; the current
message – the “dot” – will either be the first new message, or the first unread message, or
the first message of the mailbox; the option showlast will instead cause usage of the last
message for this purpose.

Messages can be printed with the print command, or short: ‘p’. By default the current
message (“dot”) is printed, but like with most other commands it is possible to give a fancy
message specification (see Specifying messages), e.g., ‘p:u’ will display all unread
messages, ‘p.’ will print the “dot”, ‘p 1 5’ will print the messages 1 and 5, ‘p 1-5’ will
print the messages 1 through 5, and ‘p-’ and ‘p+’ will print the last and the next message,
respectively.

In the default setup all header fields of a message will be printed, but this can be
changed: either by blacklisting a list of fields via ignore, or by whitelisting only a given
list with the retain command, e.g., ‘retain date from to cc subject’. In order to print all
header fields of a message regardless of currently active ignore or retain lists, use the
command Print. The variable crt controls wether and when S-nail will use the configured
PAGER for printing instead of directly writing to the terminal (generally speaking).

Dependent upon the configuration a Command line editor aims at making user experience with
the many COMMANDS a bit nicer. When reading the system mailbox or when -f (or file)
specified a mailbox explicitly prefixed with the special ‘%:’ modifier then messages which
have been read will be moved to the user's MBOX file automatically when the mailbox is left,
either by changing the active mailbox or by quitting S-nail (also see Message states).

After examining a message the user can also delete ‘d’ the message, reply ‘r’ to the sender
and all recipients or Reply ‘R’ exclusively to the sender. Messages can also be forwarded
(shorter alias is fwd). Note that when replying to or forwarding a message recipient
addresses will be stripped from comments and names unless the option fullnames is set.
Deletion causes S-nail to forget about the message; This is not irreversible, though, one
can undelete ‘u’ the message by giving its number, or the S-nail session can be ended by
giving the exit ‘x’ command.

To end a mail processing session one may either issue quit ‘q’ to cause a full program exit,
which possibly includes automatic moving of read messages to MBOX as well as updating the
[Option]al command line editor history file, or use the command exit ‘x’ instead in order to
prevent any of these actions.

Viewing HTML mail and MIME attachments
Messages which are HTML-only get more and more common and of course many messages come
bundled with a bouquet of MIME attachments. Whereas S-nail [Option]ally supports a simple
HTML-to-text converter to deal with HTML messages (see The mime.types files), it normally
can't deal with any of these itself, but instead programs need to become registered to deal
with specific MIME types or file extensions. These programs may either prepare plain text
versions of their input in order to enable S-nail to display the content on the terminal, or
display the content themselves, for example in a graphical window. The latter type of
programs by default “blocks” S-nail until the external viewer has terminated, but
asynchronous side-by-side execution is also possible, in which case S-nail will continue to
display the message and remain responsive.

To install an external handler program for a specific MIME type set an according
pipe-TYPE/SUBTYPE variable. To define a handler for a specific file extension set the
respective pipe-EXTENSION variable – these handlers take precedence. The variable
mime-counter-evidence can be set to improve dealing with faulty MIME part declarations as
are often seen in real-life messages. E.g., to display a HTML message inline (that is,
converted to a more fancy plain text representation than the builtin converter is capable to
produce) with either of the text-mode browsers lynx(1) or elinks(1), teach S-nail about
MathML documents and make it display them as plain text and to open PDF attachments in an
external PDF viewer, asynchronously:

if $features !@ HTML-FILTER
#set pipe-text/html="elinks -force-html -dump 1"
set pipe-text/html="lynx -stdin -dump -force_html"
# Display HTML as plain text instead
#set pipe-text/html=@
endif
mimetype '@ application/mathml+xml mathml'
set pipe-application/pdf="@&set -C;\
: > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\"; \
trap \"rm -f \\\"${TMPDIR}/${NAIL_FILENAME_GENERATED}\\\"\" \
EXIT INT QUIT PIPE TERM;\
set +C;\
cat > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\"; \
xpdf \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\""

Note: special care must be taken when using such commands as mail viruses may be distributed
by this method: if messages of type ‘application/x-sh’ or files with the extension ‘.sh’
were blindly filtered through the shell, for example, a message sender could easily execute
arbitrary code on the system S-nail is running on. For more on MIME, also in respect to
sending of messages, see the section The mime.types files and the command mimetype.

Mailing lists
S-nail offers some support to ease handling of mailing lists. The command mlist promotes
all given arguments to known mailing lists, and mlsubscribe sets their subscription
attribute, creating them first as necessary. (On the other hand unmlsubscribe doesn't
unmlist automatically, but only resets the subscription attribute.) Using the commands
without arguments will print out (a subset of) all currently defined mailing lists. The
headline format ‘%T’ can be used to mark out messages with configured list addresses in the
header display.

[Option]ally mailing lists may also be specified as regular expressions, which allows
matching of many addresses with a single expression. However, all fully qualified list
addresses are matched via a fast dictionary, whereas expressions are placed in (a) list(s)
which is (are) matched sequentially.

set followup-to followup-to-honour=ask-yes reply-to-honour=ask-yes
mlist a1@b1.c1 a2@b2.c2 .*@lists.c3$
mlsubscribe a4@b4.c4 exact@lists.c3

The variable followup-to-honour will ensure that a ‘Mail-Followup-To:’ header is honoured
when the message is being replied to (via reply and Lreply) and followup-to controls wether
this header is created when sending mails; it will be created automatically for a couple of
reasons, too, like when the special “mailing list specific” respond command Lreply is used,
when reply is used to respond to a message with its ‘Mail-Followup-To:’ being honoured etc.

A difference in between the handling of known and subscribed lists is that the address of
the sender is usually not part of a generated ‘Mail-Followup-To:’ when addressing the
latter, whereas it is for the former kind of lists. Usually because there are exceptions:
say, if multiple lists are addressed and not all of them are subscribed lists.

For convenience S-nail will, temporarily, automatically add a list address that is presented
in the ‘List-To:’ header of a message that is being responded to to the list of known
mailing lists. Shall that header have existed S-nail will instead, dependend on the
variable reply-to-honour, use an also set ‘Reply-To:’ for this purpose in order to accept a
list administrators' wish that is supposed to have been manifested like that (but only if it
provides a single address which resides on the same domain as what is stated in ‘List-To:’).

Resource files
Upon startup S-nail reads in several resource files:

s-nail.rc System wide initialization file. Reading of this file can be suppressed,
either by using the -n command line option, or by setting the environment
variable NAIL_NO_SYSTEM_RC.

~/.mailrc File giving initial commands. A different file can be chosen by setting the
environment variable MAILRC.

NAIL_EXTRA_RC Can be used to define an optional startup file to be read after ~/.mailrc.
This variable is only honoured in certain circumstances (see its
documentation for more).

The content of these files is interpreted as follows:

· A lines' leading whitespace is ignored.
· An empty line is ignored.
· If the line (content) starts with the number sign ‘#’ then it is a comment-command – a
real command! – and also ignored. This command is the only form of comment that is
understood.
· A line can be “continued” on the next line if the newline character is “escaped” by
preceding it with the backslash character ‘\’. Note that any leading whitespace of
follow lines is removed: If whitespace is desired it must be placed before the
backslash. For example:

# This line is a comment command. And y\
es, it is really continued here.
set debug \
verbose

Character sets
[Option] S-nail detects the character set of the terminal by using mechanisms that are
controlled by the LC_CTYPE locale setting (the manual for setlocale(3) should give an
overview); the S-nail internal variable ttycharset will be set to the detected terminal
character set accordingly and will thus show up in the output of the commands set and
varshow.

However, a user supplied ttycharset value is not overwritten by this detection mechanism:
this “feature” must be used if the detection doesn't work properly, and it may be used to
adjust the name of the locale character set. E.g., on BSD systems one may use a locale with
the character set ISO8859-1, which is not a valid name for this character set; to be on the
safe side, one may set ttycharset to the correct name, which is ISO-8859-1.

Note that changing the value doesn't mean much beside that, since several aspects of the
real character set are implied by the locale environment of the system, and that stays
unaffected by the content of an overwritten ttycharset variable. (This is mostly an issue
when interactively using S-nail, though. It is actually possible to send mail in a
completely “faked” locale environment.)

If no character set conversion capabilities have been compiled into S-nail (i.e., no
iconv(3) library has been found), then ttycharset will be the only supported character set,
it is simply assumed that it can be used to exchange 8-bit messages, and the rest of this
section does not apply; it may however still be necessary to explicitly set it if automatic
detection fails, since in that case it defaults to the mentioned ISO-8859-1.

When reading messages, their text is converted into ttycharset as necessary in order to
display them on the users terminal. Unprintable characters and invalid byte sequences are
detected and replaced by proper substitution characters (unless the variable print-all-chars
was set once S-nail was started). Also see charset-unknown-8bit to deal with another hairy
aspect of message interpretation.

When sending messages all their parts and attachments are classified. Whereas no character
set conversion is performed on those parts which appear to be binary data, the character set
being used must be declared within the MIME header of an outgoing text part if it contains
characters that do not conform to the set of characters that are allowed by the email
standards. Permissible values for character sets can be declared using the sendcharsets
variable, and charset-8bit, which defines a catch-all last-resort fallback character set
that is implicitly appended to the list of character-sets in sendcharsets.

When replying to a message and the variable reply-in-same-charset is set then the character
set of the message being replied to is tried first. And it is also possible to make S-nail
work even more closely related to the current locale setting automatically by using the
variable sendcharsets-else-ttycharset, please see there for more information.

All the specified character sets are tried in order unless the conversion of the part or
attachment succeeds. If none of the tried (8-bit) character sets is capable to represent
the content of the part or attachment, then the message will not be sent and its text will
be saved to DEAD. In general, if the message “Cannot convert from a to b” appears, either
some characters are not appropriate for the currently selected (terminal) character set, or
the needed conversion is not supported by the system. In the first case, it is necessary to
set an appropriate LC_CTYPE locale and/or the variable ttycharset.

The best results are usually achieved when S-nail is run in a UTF-8 locale on a UTF-8
capable terminal, in which case the full Unicode spectrum of characters is available. In
this setup characters from various countries can be displayed, while it is still possible to
use more simple character sets for sending to retain maximum compatibility with older mail
clients.

Message states
S-nail differentiates in between several different message states; the current state will be
reflected in the header display if headline is configured to do so. In S-nail message
states are inspected when leaving a mailbox and may cause messages to be automatically moved
to the special MBOX mailbox – because this may be irritating to users which are used to
“more modern” mail-user-agents, the default global s-nail.rc sets the hold and keepsave
variables in order to suppress this behaviour.

‘new’ Message has neither been viewed nor moved to any other state. Such messages
are retained even in the system mailbox.

‘unread’ Message has neither been viewed nor moved to any other state, but the message
was present already when the mailbox has been opened last: Such messages are
retained even in the system mailbox.

‘read’ The message has been processed by one of the following commands: ~f, ~m, ~F,
~M, copy, mbox, next, pipe, print, Print, top, type, Type, undelete. The
delete, dp, and dt commands may also cause the next message to be marked as
read, depending on the value of the autoprint variable. Except when the exit
command is used, messages that are in the system mailbox or in mailboxes which
were opened with the special ‘%:’ prefix and are in ‘read’ state when the
mailbox is left will be saved in MBOX unless the option hold it set.

‘deleted’ The message has been processed by one of the following commands: delete, dp,
dt. Only undelete can be used to access such messages.

‘preserved’ The message has been processed by a preserve command and it will be retained in
its current location.

‘saved’ The message has been processed by one of the following commands: save or write.
Unless when the exit command is used, messages that are in the system mailbox
or in mailboxes which were opened with the special ‘%:’ prefix and are in
‘saved’ state when the mailbox is left will be deleted; they will be saved in
MBOX when the option keepsave is set.

Specifying messages
Commands such as print and delete can be given a list of message numbers as arguments to
apply to a number of messages at once. Thus ‘delete 1 2’ deletes messages 1 and 2, whereas
‘delete 1-5’ will delete the messages 1 through 5. In sorted or threaded mode (see the sort
command), ‘delete 1-5’ will delete the messages that are located between (and including)
messages 1 through 5 in the sorted/threaded order, as shown in the header summary. Multiple
colon modifiers can be joined into one, e.g., ‘:du’. The following special message names
exist:

:n All ‘new’ messages.

:o All old messages (any not in state ‘read’ or ‘new’).

:u All ‘unread’ messages.

:d All ‘deleted’ messages (for the undelete command).

:r All ‘read’ messages.

:f All flagged messages.

:a All answered messages (cf. the markanswered variable).

:t All messages marked as draft.

:s [Option] All messages classified as spam.

:S [Option] All messages with unsure spam classification.

. The current message, the so-called “dot”.

; The message that was previously the current message.

, The parent message of the current message, that is the message with the Message-ID
given in the ‘In-Reply-To:’ field or the last entry of the ‘References:’ field of the
current message.

- The next previous undeleted message, or the next previous deleted message for the
undelete command. In sorted/threaded mode, the next previous such message in the
sorted/threaded order.

+ The next undeleted message, or the next deleted message for the undelete command. In
sorted/threaded mode, the next such message in the sorted/threaded order.

^ The first undeleted message, or the first deleted message for the undelete command.
In sorted/threaded mode, the first such message in the sorted/threaded order.

$ The last message. In sorted/threaded mode, the last message in the sorted/threaded
order.

&x In threaded mode, selects the message addressed with x, where x is any other message
specification, and all messages from the thread that begins at it. Otherwise it is
identical to x. If x is omitted, the thread beginning with the current message is
selected.

* All messages.

` All messages that were included in the message list for the previous command.

/string
All messages that contain string in the subject field (case ignored). See also the
searchheaders variable. If string is empty, the string from the previous
specification of that type is used again.

[@name-list]@expr
All messages that contain the given case-insensitive search expression; if the
[Option]al regular expression (see re_format(7)) support is available expr will be
interpreted as one if any of the “magical” regular expression characters is seen. If
the optional @name-list part is missing, the search is restricted to the subject field
body, but otherwise name-list specifies a comma-separated list of header fields to
search, as in

'@to,from,cc@Someone i ought to know'

In order to search for a string that includes a ‘@’ (commercial at) character the
name-list is effectively non-optional, but may be given as the empty string. Some
special header fields may be abbreviated: ‘f’, ‘t’, ‘c’, ‘b’ and ‘s’ will match
‘From’, ‘To’, ‘Cc’, ‘Bcc’ and ‘Subject’, respectively and case-insensitively. The
special names ‘header’ or ‘<’ can be used to search in (all of) the header(s) of the
message, and the special names ‘body’ or ‘>’ and ‘text’ or ‘=’ can be used to perform
full text searches – whereas the former searches only the body, the latter also
searches the message header.

This message specification performs full text comparison, but even with regular
expression support it is almost impossible to write a search expression that savely
matches only a specific address domain. To request that the content of the header is
treated as a list of addresses, and to strip those down to the plain email address
which the search expression is to be matched against, prefix the header name
(abbreviation) with a tilde ‘~’:

'@~f@@a\.safe\.domain\.match$'

address
A case-insensitive “any substring matches” search against the ‘From:’ header, which
will match addresses (too) even if showname is set (and POSIX says “any address as
shown in a header summary shall be matchable in this form”); However, if the allnet
variable is set, only the local part of the address is evaluated for the comparison,
not ignoring case, and the setting of showname is completely ignored. For finer
control and match boundaries use the ‘@’ search expression; the [Option]al IMAP-style
‘(from address)’ expression can also be used if substring matches are desired.

[Option] IMAP-style SEARCH expressions may also be used. This addressing mode is available
with all types of folders; S-nail will perform the search locally as necessary. Strings
must be enclosed by double quotes ‘"’ in their entirety if they contain white space or
parentheses; within the quotes, only backslash ‘\’ is recognized as an escape character.
All string searches are case-insensitive. When the description indicates that the
“envelope” representation of an address field is used, this means that the search string is
checked against both a list constructed as

("name" "source" "local-part" "domain-part")

for each address, and the addresses without real names from the respective header field.
These search expressions can be nested using parentheses, see below for examples.

(criterion)
All messages that satisfy the given criterion.
(criterion1 criterion2 ... criterionN)
All messages that satisfy all of the given criteria.
(or criterion1 criterion2)
All messages that satisfy either criterion1 or criterion2, or both. To connect more
than two criteria using ‘or’ specifications have to be nested using additional
parentheses, as with ‘(or a (or b c))’, since ‘(or a b c)’ really means ‘((a or b) and
c)’. For a simple ‘or’ operation of independent criteria on the lowest nesting level,
it is possible to achieve similar effects by using three separate criteria, as with
‘(a) (b) (c)’.
(not criterion)
All messages that do not satisfy criterion.
(bcc "string")
All messages that contain string in the envelope representation of the ‘Bcc:’ field.
(cc "string")
All messages that contain string in the envelope representation of the ‘Cc:’ field.
(from "string")
All messages that contain string in the envelope representation of the ‘From:’ field.
(subject "string")
All messages that contain string in the ‘Subject:’ field.
(to "string")
All messages that contain string in the envelope representation of the ‘To:’ field.
(header name "string")
All messages that contain string in the specified ‘Name:’ field.
(body "string")
All messages that contain string in their body.
(text "string")
All messages that contain string in their header or body.
(larger size)
All messages that are larger than size (in bytes).
(smaller size)
All messages that are smaller than size (in bytes).
(before date)
All messages that were received before date, which must be in the form
‘d[d]-mon-yyyy’, where ‘d’ denotes the day of the month as one or two digits, ‘mon’ is
the name of the month – one of ‘Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec’, and
‘yyyy’ is the year as four digits, e.g., ‘28-Dec-2012’.
(on date)
All messages that were received on the specified date.
(since date)
All messages that were received since the specified date.
(sentbefore date)
All messages that were sent on the specified date.
(senton date)
All messages that were sent on the specified date.
(sentsince date)
All messages that were sent since the specified date.
() The same criterion as for the previous search. This specification cannot be used as
part of another criterion. If the previous command line contained more than one
independent criterion then the last of those criteria is used.

On URL syntax and credential lookup
[v15-compat] For accessing protocol-specific resources, like POP3 mailboxes, usage of
compact and standardized Uniform Resource Locators (URL, RFC 1738) has become omnipresent.
S-nail expects and understands URLs in the following form; parts in brackets ‘[]’ denote
optional parts, optional either because there also exist other ways to define the
information in question or because support of the part is protocol-specific – e.g., ‘/path’
is used by the IMAP protocol but not by POP3.

PROTOCOL://[USER[:PASSWORD]@]server[:port][/path]

If ‘USER’ and ‘PASSWORD’ are specified as part of an URL they must be given in URL percent
encoded (RFC 3986) form – the command urlencode can be used to perform the encoding and show
the encoded value. (This doesn't really conform to any standard, but for one it isn't used
for any data exchange over the internet, and second it's easier for users to simply call
urlencode on a string and use that instead of having to deal with several different
standards.) On the other hand, values given in variables are expected not to be URL percent
encoded.

Many variable options of S-nail exist in multiple versions, called variable chains for the
rest of this document: the plain ‘variable’ as well as ‘variable-HOST’ and
‘variable-USER@HOST’. Here ‘HOST’ indeed means ‘server:port’ if a ‘port’ had been specified
in the respective URL, otherwise it refers to the plain ‘server’. Also, ‘USER’ isn't truly
the ‘USER’ that had been found when doing the user chain lookup as is described below, i.e.,
this ‘USER’ will never be in URL percent encoded form, wether it came from an URL or not.

For example, wether an hypothetical URL ‘smtp://hey%3Ayou@our.house’ had been given that
includes a user, or wether the URL was ‘smtp://our.house’ and the user had been found
differently, to lookup the variable chain smtp-use-starttls S-nail first looks for wether
‘smtp-use-starttls-hey:you@our.house’ is defined, then wether ‘smtp-use-starttls-our.house’
exists before finally ending up looking at the plain variable itself.

S-nail obeys the following logic scheme when dealing with the necessary credential
informations of an account:

· If no ‘USER’ has been given in the URL the variables user-HOST and user are looked up;
if no such variable(s) can be found then S-nail will, when enforced by the [Option]al
variables netrc-lookup-HOST or netrc-lookup, search the users .netrc file for a ‘HOST’
specific entry which provides a ‘login’ name: this lookup will only succeed if
unambiguous (one possible matching entry for ‘HOST’).

If there is still no ‘USER’ then S-nail will fall back to the user who is supposed to
run S-nail: either the name that has been given with the -u command line option (or,
equivalently, but with less precedence, the environment variable USER), or the “current”
user. The identity of this user has been fixated during S-nail startup and is known to
be a valid user on the current host.

· Authentication: unless otherwise noted this will lookup the PROTOCOL-auth-USER@HOST,
PROTOCOL-auth-HOST, PROTOCOL-auth variable chain, falling back to a protocol-specific
default should this have no success.

· If no ‘PASSWORD’ has been given in the URL – it should be noted once that specifying the
password in the URL is only syntactic sugar for the user, it'll never be part of an URL
that S-nail uses itself –, then if the ‘USER’ has been found through the [Option]al
.netrc file lookup then that may have already provided the password, too. Otherwise the
variable chain password-USER@HOST, password-HOST, password is looked up.

[Option] Then if any of the variables of the chain agent-shell-lookup-USER@HOST,
agent-shell-lookup-HOST, agent-shell-lookup is set the shell command specified therein
is run and the output (less newline characters) will be used as the password. It is
perfectly valid for such an agent to simply not return any data, in which case the
password lookup is continued somewhere else; Any command failure is treated as a hard
error, however.

The next variable chain that is inspected is the [Option]al netrc-lookup-USER@HOST,
netrc-lookup-HOST, netrc-lookup, but this time looking only for the password (multiple
user accounts for a single machine may exist as well as a fallback entry without user
but with a password).

If at that point there is still no password available, but the (protocols') chosen
authentication type requires a password, then in interactive mode the user will be
prompted on the terminal.

Note: S/MIME verification works relative to the values found in the ‘From:’ (or ‘Sender:’)
header field(s), which means that the values of smime-sign, smime-sign-cert,
smime-sign-include-certs and smime-sign-message-digest will not be looked up using the
‘USER’ and ‘HOST’ chains from above but instead use the corresponding values from the
message that is being worked on. In unusual cases multiple and different ‘USER’ and ‘HOST’
combinations may therefore be involved – on the other hand those unusual cases become
possible. The usual case is as short as:

set smtp=smtp://USER:PASS@HOST smtp-use-starttls \
smime-sign smime-sign-cert=+smime.pair

The section EXAMPLES contains complete example configurations.

Command line editor
[Option] S-nail can be configured to support a command line editor and command history lists
which are saved in between sessions. One may link against fully-fledged external libraries
(readline(6), editline(3)) or use S-nail's own command line editor NCL (Nail-Command-Line)
instead, which should work in all environments which comply to the ISO C standard (ISO/IEC
9899:1990/Amendment 1:1995). When an external library is used, interactive behaviour of
S-nail relies on that library and may not correspond one-to-one to what is described in this
manual.

Regardless of the actually used command line editor history entries will be created for
lines entered in command mode only, and creation of such an entry can be forcefully
suppressed by starting the line with a space character. Note that history handling is by
itself an optional feature and may therefore not be available. For more information see the
documentation of the options emptystart, history-gabby, history-gabby-persist,
line-editor-disable, NAIL_HISTFILE and NAIL_HISTSIZE.

The builtin S-nail command line editor supports the following operations; the notation
‘^-character’ stands for the combination of the “Control” key plus the mentioned character,
e.g., ‘^A’ means “hold down control key and press the A key”:

‘^A’ Go to the start of the line.
‘^B’ Move the cursor backward one character.
‘^D’ Forward delete the character under the cursor; quits S-nail if used on the empty line
unless the ignoreeof option is set.
‘^E’ Go to the end of the line.
‘^F’ Move the cursor forward one character.
‘^G’ Cancel current operation, full reset. If there is an active history search or
tabulator expansion then this command will first reset that, reverting to the former
line content; thus a second reset is needed for a full reset in this case. In all
cases S-nail will reset a possibly used multibyte character input state machine.
‘^H’ The same as “backspace”: backward delete one character.
‘^I’ [Option] The same as “horizontal tabulator”: try to expand the word before the
cursor. (Note this is not “tabulator-completion” as is known from the sh(1) but
really means the usual S-nail expansion, as documented for file, yet it involves
shell expansion as a last step, too.)
‘^J’ The same as “ENTER”: complete this line of input.
‘^K’ Delete all characters from the cursor to the end of the line.
‘^L’ Repaint the line.
‘^N’ [Option] Go to the next history entry.
‘^O’ Execute the command dp.
‘^P’ [Option] Go to the previous history entry.
‘^R’ [Option] Complete the current line from (the remaining older) history entries.
‘^U’ The same as ‘^A’ followed by ‘^K’.
‘^W’ Delete the characters from the one preceding the cursor to the preceding word
boundary.
‘^X’ Move the cursor forward one word boundary.
‘^Y’ Move the cursor backward one word boundary.

If problems with commands that are based upon rightwise movement are encountered,
adjustments of the option line-editor-cursor-right may solve the problem, as documented for
it.

If the terminal produces key sequences which are compatible with xterm(1) then the left and
right cursor keys will map to ‘^B’ and ‘^F’, respectively, the up and down cursor keys will
map to ‘^P’ and ‘^N’, and the Home/End/PgUp/PgDown keys will call the z command with the
respective arguments ‘0’, ‘$’, ‘-’ and ‘+’ (i.e., perform scrolling through the header
summary list).

Coloured message display
[Option] S-nail can be configured to support coloured message display, realized by emitting
ANSI colour escape sequences. Colours are only used when the TERM environment variable is
set and either the terminal type can be found in colour-terms or its name includes the
string ‘color’.

On top of that the binary option colour-pager defines wether these colour sequences are also
generated when the output of a command needs to go through the PAGER (also see crt) – this
is not enabled by default because different pager programs need different command line
switches or other configuration in order to support those colour sequences, please see the
option for more details.

To forcefully disable all colour support, set colour-disable.

Colours can be configured through font attributes (‘ft=’ – ‘bold’, ‘invers’ and
‘underline’), foreground (‘fg=’) and background (‘bg=’) colours (‘black’, ‘blue’, ‘green’,
‘red’, ‘brown’, ‘magenta’, ‘cyan’ and ‘white’). Multiple specifications can be joined in a
comma separated list, as in

set colour-msginfo="ft=bold,fg=magenta,bg=cyan"

Options to be set are colour-msginfo, colour-partinfo, colour-from_, colour-header and
colour-uheader, as well as colour-user-headers, which is a list of headers to be colourized
via colour-uheader instead of the default colour-header.

COMMANDS


Each command is typed on a line by itself, and may take arguments following the command
word. The command need not be typed in its entirety – the first command which matches the
typed prefix is used. (The command list prints a sorted list of available commands, and the
command help (or ?), when given an argument, will show a documentation string for the
expansion, as in ‘?unc’; documentation strings are however [Option]al.)

For commands which take message lists as arguments, the next message forward that satisfies
the command's requirements will be used shall no explicit message list have been passed. If
there are no messages forward of the current message, the search proceeds backwards, and if
there are no good messages at all, S-nail types “no applicable messages” and aborts the
command. The arguments to commands can be quoted, using the following methods:

· An argument can be enclosed between paired double-quotes ‘"argument"’ or single-
quotes ‘'argument'’; any white space, shell word expansion, or backslash
characters (except as described next) within the quotes are treated literally as
part of the argument. A double-quote will be treated literally within single-
quotes and vice versa. Inside such a quoted string the actually used quote
character can be used nonetheless by escaping it with a backslash ‘\’, as in
‘"y\"ou"’.
· An argument that is not enclosed in quotes, as above, can usually still contain
space characters if those spaces are backslash-escaped.
· A backslash outside of the enclosing quotes is discarded and the following
character is treated literally as part of the argument.
· An unquoted backslash at the end of a command line is discarded and the next line
continues the command.

Filenames, where expected, are subsequently subjected to the following transformations, in
sequence:

· If the filename begins with an unquoted plus sign, and the folder variable is
defined, the plus sign will be replaced by the value of the folder variable
followed by a slash. If the folder variable is unset or is set to null, the
filename will be unchanged.
· Shell word expansions are applied to the filename. Compatibility note: on the
long run support for complete shell word expansion will be replaced by an
internally implemented restricted expansion mechanism in order to circumvent
possible security impacts through shell expansion. Expect that a growing number
of program parts only support this restricted syntax:

Meta expansions are applied to the filename: leading tilde characters (‘~/’) will
be replaced by the expansion of HOME, and any occurrence of ‘$VARIABLE’ (or
‘${VARIABLE}’) will be replaced by the expansion of the variable, if possible;
S-nail internal as well as environmental (shell) variables can be accessed through
this mechanism. In order to include a raw ‘$’ character precede it with a
backslash ‘\’, to include a backslash double it. If more than a single pathname
results from this expansion and the command is expecting one file, an error
results.

Note that in interactive display context, in order to allow simple value
acceptance (typing “ENTER”), backslash quoting is performed automatically as
necessary, e.g., a file ‘diet\ is \curd.txt’ will be displayed as ‘diet\\ is
\\curd.txt’.

The following commands are available:

# The comment-command causes the entire line to be ignored. Note: this really is a
normal command which' purpose is to discard its arguments, not a “comment-start”
indicating special character, which means that, e.g., trailing comments on a line
are not possible.

~ Interprets the remainder of the word as a macro name and passes it through to the
call command; e.g., ‘~mymacro’ is a shorter synonym for ‘call mymacro’.

- Print out the preceding message. If given a numeric argument n, goes to the n'th
previous message and prints it.

= Show the current message number (the “dot”).

? Prints a brief summary of commands. [Option] Given an argument a synopsis for the
command in question is printed instead; commands can be abbreviated in general and
this command can be used to see the full expansion of an abbreviation including the
synopsis, try, e.g., ‘?h’, ‘?hel’ and ‘?help’ and see how the display changes.

! Executes the SHELL (see sh(1)) command which follows.

| A synonym for the pipe command.

account (ac) Creates, selects or lists (an) account(s). An account is a group of commands
and variable settings which together usually arrange the environment for the
purpose of creating a system login. Without any argument a listing of all defined
accounts and their content is printed. A specific account can be activated by
giving solely its name, resulting in the system mailbox or inbox of that account to
be activated as via an explicit use of the command file. The two argument form is
identical to defining a macro as via define. For example:

account myisp {
set folder=imaps://mylogin@imap.myisp.example
set record=+Sent
set from="myname@myisp.example (My Name)"
set smtp=smtp://mylogin@smtp.myisp.example
}

creates an account named ‘myisp’ which can later be selected by specifying ‘account
myisp’. The special account ‘null’ (case-insensitive) always exists. localopts
can be used to localize account settings – different to normal macros the settings
will be reverted once the account is switched off. Accounts can be deleted via
unaccount.

alias (a) With no arguments, prints out all currently-defined aliases. With one
argument, prints out that alias. With more than one argument, creates a new alias
or appends to an existing one. unalias can be used to delete aliases.

alternates
(alt) Manage a list of alternate addresses / names of the active user, members of
which will be removed from recipient lists when replying to messages (and the metoo
variable is not set). If arguments are given the set of alternate names is
replaced by them, without arguments the current set is displayed.

answered
Takes a message list and marks each message as having been answered. This mark has
no technical meaning in the mail system; it just causes messages to be marked in
the header summary, and makes them specially addressable.

cache [Option] Only applicable to cached IMAP mailboxes; takes a message list and reads
the specified messages into the IMAP cache.

call Calls a macro that has been created via define.

cd (ch) Change the working directory to HOME or the given argument. Synonym for
chdir.

certsave
[Option] Only applicable to S/MIME signed messages. Takes a message list and a
file name and saves the certificates contained within the message signatures to the
named file in both human-readable and PEM format. The certificates can later be
used to send encrypted messages to the respective message senders by setting
smime-encrypt-USER@HOST variables.

chdir (ch) Change the working directory to HOME or the given argument. Synonym for cd.

collapse
Only applicable to threaded mode. Takes a message list and makes all replies to
these messages invisible in header summaries, unless they are in state ‘new’.

connect [Option] If operating in disconnected mode on an IMAP mailbox, switch to online
mode and connect to the mail server while retaining the mailbox status. See the
description of the disconnected variable for more information.

Copy (C) Copy messages to files whose names are derived from the author of the
respective message and don't mark them as being saved; otherwise identical to Save.

copy (c) Copy messages to the named file and don't mark them as being saved; otherwise
identical to save.

cwd Print the current working directory.

Decrypt [Option] For unencrypted messages this command is identical to Copy; Encrypted
messages are first decrypted, if possible, and then copied.

decrypt [Option] For unencrypted messages this command is identical to copy; Encrypted
messages are first decrypted, if possible, and then copied.

define Without arguments the current list of macros, including their content, is printed,
but otherwise a macro is defined. A macro definition is a sequence of commands in
the following form:

define name {
command1
command2
...
commandN
}

A defined macro can be invoked explicitly by using the call or ~ commands, or
implicitly by setting the folder-hook or folder-hook-FOLDER variables. Note that
interpretation of localopts depends on how (i.e., “as what”: normal macro, folder
hook, account switch) the macro is invoked. Macros can be deleted via undefine.

delete (d) Marks the given message list as ‘deleted’. Deleted messages will neither be
saved in MBOX nor will they be available for most other commands.

discard (di) Identical to ignore. Also see retain.

disconnect
[Option] (disco) If operating in online mode on an IMAP mailbox, switch to
disconnected mode while retaining the mailbox status. See the description of the
disconnected variable for more. A list of messages may optionally be given as
argument; the respective messages are then read into the cache before the
connection is closed. Thus `disco *' makes the entire mailbox available for
disconnected use.

dp, dt Deletes the current message and prints the next message. If there is no next
message, S-nail says “at EOF”.

draft Takes a message list and marks each given message as a draft. This mark has no
technical meaning in the mail system; it just causes messages to be marked in the
header summary, and makes them specially addressable.

echo (ec) Echoes its arguments, resolving special names as documented for the command
file. The escape sequences ‘\a’, ‘\b’, ‘\c’, ‘\f’, ‘\n’, ‘\r’, ‘\t’, ‘\v’, ‘\\’
and ‘\0octal-num’ are interpreted just as they are by printf(1) (proper quoting
provided).

edit (e) Point the text editor (as defined in EDITOR) at each message from the given
list in turn. Modified contents are discarded unless the writebackedited variable
is set.

elif Part of the if/elif/else/endif conditional — if the condition of a preceeding if
was false, check the following condition and execute the following block if it
evaluates true.

else (el) Part of the if/elif/else/endif conditional — if none of the conditions of the
preceeding if and elif commands was true, the else block is executed.

endif (en) Marks the end of an if/elif/else/endif conditional execution block.

errors [Option] Since S-nail uses the console as a user interface it can happen that
messages scroll by too fast to become recognized. Optionally an error message ring
queue is available which stores duplicates of any error message and notifies the
user in interactive sessions whenever a new error has occurred. The queue is
finite: if its maximum size is reached any new message replaces the eldest. The
command errors can be used to manage this message queue: if given show or no
argument the queue will be displayed and cleared, clear will only clear all
messages from the queue.

exit (ex or x) Exit from S-nail without changing the active mailbox and skip any saving
of messages in MBOX as well as a possibly tracked command line editor history file.

features
Print the list of features that have been compiled into S-nail.

File (Fi) Like file, but open the mailbox readonly.

file (fi) The file command switches to a new mailbox. Without arguments it prints the
complete state of the current mailbox. If an argument is given, it will write out
changes (such as deletions) the user has made and open a new mailbox. Some special
conventions are recognized for the name argument:

# (number sign) means the previous file,
% (percent sign) means the invoking user's system mailbox (or the
value of folder for IMAP folders),
%user means the system mailbox of user (and never the value of folder,
regardless of its actual setting),
& (ampersand) means the invoking user's MBOX file and
+file means a file in the folder directory.
%:filespec expands to the same value as filespec, but the file is handled as
a system mailbox by, e.g., the mbox and save commands, meaning
that messages that have been read in the current session will be
moved to the MBOX mailbox instead of simply being flagged as
read.

If the name matches one of the strings defined with the command shortcut, it is
replaced by its long form and expanded. If the name ends with ‘.gz’, ‘.bz2’ or
‘.xz’ it is treated as being compressed with gzip(1), bzip2(1) or xz(1),
respectively, and transparently handled through an intermediate (un)compression
step (using a temporary file) with the according facility, sufficient support
provided. Likewise, if the named file doesn't exist, but a file with one of the
mentioned compression extensions does, then the name is automatically expanded and
the compressed file is used.

Otherwise, if the name ends with an extension for which file-hook-load-EXTENSION
and file-hook-save-EXTENSION variables are set, then the given hooks will be used
to load and save “name”, and S-nail will work with an intermediate temporary file.

MBOX files (flat file-based mailboxes) are generally locked during file operations
in order to avoid inconsistencies against concurrent modifications. Mailbox files
which S-nail treats as system mailboxes will also be protected by so-called dotlock
files, the traditional way of mail spool file locking: for any file ‘a’ a lock file
‘a.lock’ will be created for the duration of the synchronization — as necessary a
privilege-separated dotlock child process will be used to accommodate for necessary
privilege adjustments in order to create the dotlock file in the same directory and
with the same user and group identities as the file of interest. Also see
mbox-rfc4155 for fine-tuning the handling of MBOX files.

If name refers to a directory with the subdirectories ‘tmp’, ‘new’ and ‘cur’, then
it is treated as a folder in “Maildir” format. A name of the form

[v15-compat] protocol://[user[:password]@]host[:port][/path]
[no v15-compat] protocol://[user@]host[:port][/path]

is taken as an Internet mailbox specification. The [Option]ally supported
protocols are pop3 (POP3) and pop3s (POP3 with SSL/TLS encrypted transport). The
[/path] part is valid only for IMAP; there it defaults to INBOX. Also see the
section On URL syntax and credential lookup.

[no v15-compat] If user contains special characters, in particular ‘/’ or ‘%’, they
must be escaped in URL notation – the command urlencode can be used to show the
necessary conversion. The optional `path' part applies to IMAP only; if it is
omitted, the default `INBOX' is used.

If S-nail is connected to an IMAP server, a name of the form `@mailbox' refers to
the `mailbox' on that server, but otherwise a `@' prefix has no special meaning.

flag Takes a message list and marks the messages as flagged for urgent/special
attention. This mark has no technical meaning in the mail system; it just causes
messages to be highlighted in the header summary, and makes them specially
addressable.

folder (fold) The same as file.

folders With no arguments, list the names of the folders in the folder directory. With an
existing folder as an argument, lists the names of folders below the named folder;
e.g. the command `folders @' lists the folders on the base level of the current
IMAP server. See also the variable imap-list-depth.

Followup
(F) Similar to Respond, but saves the message in a file named after the local part
of the first recipient's address (instead of in record).

followup
(fo) Similar to respond, but saves the message in a file named after the local part
of the first recipient's address (instead of in record).

followupall
Similar to followup, but responds to all recipients regardless of the flipr
variable.

followupsender
Similar to Followup, but responds to the sender only regardless of the flipr
variable.

Forward Alias for Fwd.

forward Alias for fwd.

from (f) Takes a list of messages and prints their message headers (which qualifies this
command as S-nails search facility).

Fwd Similar to fwd, but saves the message in a file named after the local part of the
recipient's address (instead of in record).

fwd Takes a message and the address of a recipient and forwards the message to him.
The text of the original message is included in the new one, with the value of the
fwdheading variable printed before. The fwdignore and fwdretain commands specify
which header fields are included in the new message. Only the first part of a
multipart message is included unless the forward-as-attachment option is set.
Unless the option fullnames is set recipient addresses will be stripped from
comments, names etc.

fwdignore
Specifies which header fields are to be ignored with the command fwd. This command
has no effect when the forward-as-attachment option is set.

fwdretain
Specifies which header fields are to be retained with the command fwd. fwdretain
overrides fwdignore. This command has no effect when the forward-as-attachment
option is set.

ghost Define or list command aliases, so-called ghosts. Without arguments a list of all
currently known aliases is printed. With one argument the expansion of the given
alias is shown. With two or more arguments a command alias is defined or updated:
the first argument is the name under which the remaining command line should be
accessible, the content of which can be just about anything. A ghost can be used
everywhere a normal command can be used, but always takes precedence; any arguments
that are given to the command alias are joined onto the alias content, and the
resulting string forms the command line that is, in effect, executed. Also see
unghost.

? gh xx
`ghost': no such alias: "xx"
? gh xx echo hello,
? gh xx
ghost xx "echo hello,"
? xx
hello,
? xx world
hello, world

headers (h) Show the current group of headers, the size of which depends on the variable
screen. If a message-specification is given the group of headers containing the
first message therein is shown and the message at the top of the screen becomes the
new “dot”.

help (hel) A synonym for ?.

history [Option] Either show or clear the list of history entries; a decimal NUMBER
argument selects and shows the respective history entry – press “ENTER” to accept
it, and the history entry will become the new history top. The default mode if no
arguments are given is show.

hold (ho, also preserve) Takes a message list and marks each message therein to be saved
in the user's system mailbox instead of in MBOX. Does not override the delete
command. S-nail deviates from the POSIX standard with this command, because a next
command issued after hold will display the following message, not the current one.

if (i) Part of the nestable if/elif/else/endif conditional execution construct — if
the given condition is true then the encapsulated block is executed. POSIX only
supports the conditions ‘[Rr]eceive’, ‘[Ss]end’ and ‘[Tt]erm’ (execute if standard
input is a tty), all remaining conditions are non-portable extensions; note that
falsely specified conditions cause the execution of the entire conditional
construct until the (matching) closing endif command to be suppressed. The syntax
of the nestable if conditional execution construct requires that each condition and
syntax element is surrounded by whitespace.

if receive
commands ...
else
commands ...
endif

Another condition can be any boolean value (see the section Value options for
booleans) to mark an enwrapped block as “never execute” or “always execute”. It is
possible to check a variable for existence or compare its expansion against a user
given value or another variable via the ‘$’ (“variable next”) conditional trigger
character. The available comparison operators are ‘<’ (less than), ‘<=’ (less than
or equal to), ‘==’ (equal), ‘!=’ (not equal), ‘>=’ (greater than or equal to), ‘>’
(greater than), ‘=@’ (is substring of) and ‘!@’ (is not substring of). The values
of the left and right hand side are treated as strings and are compared 8-bit byte-
wise, ignoring case according to the rules of the US-ASCII encoding (therefore,
dependend on the active locale, possibly producing false results for strings in the
locale encoding). Except for the substring checks the comparison will instead be
performed arithmetically if both, the user given value as well as the variable
content, can be parsed as numbers (integers). An unset variable is treated as the
empty string.

When the [Option]al regular expression support is available, the additional test
cases ‘=~’ and ‘!~’ can be used. They treat the right hand side as a regular
expression that is matched case-insensitively and according to the active LC_CTYPE
locale, meaning that strings in the locale encoding should be matched correctly.

Conditions can be joined via AND-OR lists (where the AND operator is ‘&&’ and the
OR operator is ‘||’), which have equal precedence and will be evaluated with left
associativity, thus using the same syntax that is known for the sh(1). It is also
possible to form groups of conditions and lists by enclosing them in pairs of
brackets ‘[ ... ]’, which may be interlocked within each other, and also be joined
via AND-OR lists.

The results of individual conditions and entire groups may be modified via unary
operators: the unary operator ‘!’ will reverse the result.

if $debug
echo *debug* is set
endif
if $ttycharset == "UTF-8"
echo *ttycharset* is set to UTF-8, case-insensitively
endif
set t1=one t2=one
if $t1 == $t2
echo These two variables are equal
endif
if $version-major >= 15
echo Running a new version..
if $features =@ "regex"
if $TERM =~ "^xterm.*"
echo ..in an X terminal
endif
endif
if [ [ true ] && [ [ $debug ] || [ $verbose ] ] ]
echo Noisy, noisy
endif
if true && $debug || $verbose
echo Left associativity, as is known from the shell
endif
if ! ! true && ! [ ! $debug && ! $verbose ]
echo Unary operator support
endif
endif

ignore Without arguments the list of ignored header fields is printed, otherwise the given
list of header fields is added to the ignore list: Header fields in the ignore list
are not printed on the terminal when a message is printed. To print a message in
its entirety, use the commands Type or Print. Also see discard and retain.

imap [Option] Sends command strings directly to the current IMAP server. S-nail
operates always in IMAP `selected state' on the current mailbox; commands that
change this will produce undesirable results and should be avoided. Useful IMAP
commands are:

create Takes the name of an IMAP mailbox as an argument and creates
it.

getquotaroot (RFC 2087) Takes the name of an IMAP mailbox as an argument
and prints the quotas that apply to the mailbox. Not all IMAP
servers support this command.

namespace (RFC 2342) Takes no arguments and prints the Personal
Namespaces, the Other User's Namespaces and the Shared
Namespaces. Each namespace type is printed in parentheses; if
there are multiple namespaces of the same type, inner
parentheses separate them. For each namespace a prefix and a
hierarchy separator is listed. Not all IMAP servers support
this command.

inc Same as newmail.

list Prints the names of all available commands, alphabetically sorted.

localopts
This command can be used to localize changes to variables, meaning that their state
will be reverted to the former one once the covered scope is left. It can only be
used inside of macro definition blocks introduced by account or define, and is
interpreted as a boolean (see Value options); the “covered scope” of an account is
left once it is switched off again.

define temporary_settings {
set global_option1
localopts on
set local_option1
set local_option2
localopts off
set global_option2
}

Note that this setting “stacks up”: i.e., if ‘macro1’ enables change localization
and calls ‘macro2’, which explicitly resets localization, then any value changes
within ‘macro2’ will still be reverted by ‘macro1’!

Lreply Reply to messages that come in via known (mlist) or subscribed (mlsubscribe)
mailing lists, or pretend to do so (see Mailing lists): on top of the usual reply
functionality this will actively resort and even remove message recipients in order
to generate a message that is supposed to be send to a mailing list. For example
it will also implicitly generate a ‘Mail-Followup-To:’ header if that seems useful,
regardless of the setting of the variable followup-to.

Mail Similar to mail, but saves the message in a file named after the local part of the
first recipient's address (instead of in record).

mail (m) Takes a (list of) recipient address(es) as (an) argument(s), or asks on
standard input if none were given; then collects the remaining mail content and
sends it out.

mbox (mb) The given message list is to be sent to MBOX when S-nail is quit; this is the
default action unless the hold option is set. [v15 behaviour may differ] This
command can only be used in a system mailbox (see file).

mimetype
Without any arguments the content of the MIME type cache will displayed. Otherwise
each argument defines a complete MIME type specification of a type that shall be
added (prepended) to the cache. In any event MIME type sources are loaded first as
necessary – mimetypes-load-control can be used to fine-tune which sources are
actually loaded. Refer to the section on The mime.types files for more on MIME
type specifications and this topic in general. MIME type unregistration and cache
resets can be triggered with unmimetype.

mlist Without arguments the list of all currently defined mailing lists (and their
attributes, if any) is printed. Otherwise all given arguments (which need not be
quoted except for whitespace) will be added and henceforth be recognized as mailing
lists. Mailing lists may be removed via the command unmlist.

If the [Option]al regular expression support is available then mailing lists may
also be specified as regular expressions (see re_format(7) for more on those).

mlsubscribe
Without arguments the list of all currently defined mailing lists which have a
subscription attribute is printed. Otherwise this attribute will be set for all
given mailing lists, newly creating them as necessary (as via mlist). Subscription
attributes may be removed via the command unmlsubscribe. Also see followup-to.

Move Similar to move, but moves the messages to a file named after the local part of the
sender address of the first message (instead of in record).

move Acts like copy but marks the messages for deletion if they were transferred
successfully.

More Like more, but also prints ignored header fields and all MIME parts. Identical to
Page.

more Invokes the PAGER on the given messages, even in non-interactive mode and as long
as the standard output is a terminal. Identical to page.

netrc [Option] Either (show or) clear the current .netrc cache, loading the file first as
necessary in the former case. Note that S-nail will try to read the file only
once, use ‘netrc clear’ to unlock the next attempt. See netrc-lookup and the
section On URL syntax and credential lookup; the section The .netrc file documents
the file format in detail.

newmail Checks for new mail in the current folder without committing any changes before.
If new mail is present, a message is printed. If the header variable is set, the
headers of each new message are also printed.

next (n) (like ‘+’ or “ENTER”) Goes to the next message in sequence and types it. With
an argument list, types the next matching message.

New Same as Unread.

new Same as unread.

noop If the current folder is accessed via a network connection, a “NOOP” command is
sent, otherwise no operation is performed.

Page Like page, but also prints ignored header fields and all MIME parts. Identical to
More.

page Invokes the PAGER on the given messages, even in non-interactive mode and as long
as the standard output is a terminal. Identical to more.

Pipe Like pipe but also pipes ignored header fields and all parts of MIME
‘multipart/alternative’ messages.

pipe (pi) Takes a message list and a shell command and pipes the messages through the
command. Without an argument the current message is piped through the command
given by the cmd variable. If the page variable is set, every message is followed
by a formfeed character.

preserve
(pre) A synonym for hold.

Print (P) Like print but also prints out ignored header fields and all parts of MIME
‘multipart/alternative’ messages. See also print, ignore and retain.

print (p) Takes a message list and types out each message on the user's terminal. For
MIME multipart messages, all parts with a content type of ‘text’ or ‘message’ are
shown, the other are hidden except for their headers. Messages are decrypted and
converted to the terminal character set if necessary.

quit (q) Terminates the session, saving all undeleted, unsaved messages in the current
MBOX, preserving all messages marked with hold or preserve or never referenced in
the system mailbox, and removing all other messages from the system mailbox. If
new mail has arrived during the session, the message “You have new mail” will be
shown. If given while editing a mailbox file with the command line flag -f, then
the edit file is rewritten. A return to the shell is effected, unless the rewrite
of edit file fails, in which case the user can escape with the exit command.

redirect
Same as resend.

Redirect
Same as Resend.

remove Removes the named folders. The user is asked for confirmation in interactive mode.

rename Takes the name of an existing folder and the name for the new folder and renames
the first to the second one. Both folders must be of the same type and must be
located on the current server for IMAP.

Reply (R) Reply to originator. Does not reply to other recipients of the original
message. flipr will exchange this command with reply. Unless the option fullnames
is set the recipient address will be stripped from comments, names etc.

reply (r) Take a message and group-responds to it by addressing the sender and all
recipients. followup-to, followup-to-honour, reply-to-honour as well as
recipients-in-cc influence response behaviour. The command Lreply offers special
support for replying to mailing lists. Unless the option fullnames is set
recipient addresses will be stripped from comments, names etc. If flipr is set the
commands Reply and reply are exchanged.

replyall
Similar to reply, but initiates a group-reply regardless of the value of flipr.

replysender
Similar to Reply, but responds to the sender only regardless of the value of flipr.

Resend Like resend, but does not add any header lines. This is not a way to hide the
sender's identity, but useful for sending a message again to the same recipients.

resend Takes a list of messages and a user name and sends each message to the named user.
‘Resent-From:’ and related header fields are prepended to the new copy of the
message.

Respond Same as Reply.

respond Same as reply.

respondall
Same as replyall.

respondsender
Same as replysender.

retain (ret) Without arguments the list of retained header fields is printed, otherwise
the given list of header fields is added to the retain list: Header fields in the
retain list are shown on the terminal when a message is printed, all other header
fields are suppressed. To print a message in its entirety, use the commands Type
or Print. Also see discard and ignore; retain takes precedence over the mentioned.

Save (S) Similar to save, but saves the messages in a file named after the local part of
the sender of the first message instead of (in record and) taking a filename
argument.

save (s) Takes a message list and a filename and appends each message in turn to the end
of the file. If no filename is given, the MBOX file is used. The filename in
quotes, followed by the generated character count is echoed on the user's terminal.
If editing a system mailbox the messages are marked for deletion. Compressed files
and IMAP mailboxes are handled as described for the -f command line option above.

savediscard
Same as saveignore.

saveignore
Is to save what ignore is to print and type. Header fields thus marked are
filtered out when saving a message by save or when automatically saving to MBOX.
This command should only be applied to header fields that do not contain
information needed to decode the message, as MIME content fields do. If saving
messages on an IMAP account ignoring fields makes it impossible to copy the data
directly on the server, thus operation usually becomes much slower.

saveretain
Is to save what retain is to print and type. Header fields thus marked are the
only ones saved with a message when saving by save or when automatically saving to
MBOX. saveretain overrides saveignore. The use of this command is strongly
discouraged since it may strip header fields that are needed to decode the message
correctly.

seen Takes a message list and marks all messages as having been read.

set (se) Without arguments this command prints all options and, for non-binary options,
values that are currently known to S-nail. Setting any of the options bsdcompat or
bsdset changes the output format to BSD style, otherwise a properly quoted listing
is produced. If debug is set or verbose has been set twice then the listing is
modified to mark out assembled variables.

Otherwise modifies (set and unsets) the given options. Arguments are of the form
‘option=value’ (no space before or after ‘=’), or plain ‘option’ if there is no
value. Quotation marks may be placed around any part of the assignment statement
to quote blanks or tabs, e.g.,

set indentprefix="->"

If an argument begins with ‘no’, as in ‘set nosave’, the effect is the same as
invoking the unset command with the remaining part of the variable (‘unset save’).

setenv Identical to set except that the options are also exported into the program
environment; since this task requires native host support the command will always
report error if that is not available (but still act like set in this case). This
operation is a no-op unless all resource files have been loaded. Also see
unsetenv.

shell (sh) Invokes an interactive version of the shell.

shortcut
Without arguments the list of all currently defined shortcuts is printed.
Otherwise all given arguments (which need not be quoted except for whitespace) are
treated as pairs of shortcuts and their expansions, creating new or changing
already existing shortcuts, as necessary. Shortcuts may be removed via the command
unshortcut. The expansion strings should be in the syntax that has been described
for the file command.

show Like print, but performs neither MIME decoding nor decryption, so that the raw
message text is shown.

size (si) Print the size in characters of each message of the given message-list.

sort Create a sorted representation of the current folder, and change the next command
and the addressing modes such that they refer to messages in the sorted order.
Message numbers are the same as in regular mode. If the header variable is set, a
header summary in the new order is also printed. Possible sorting criteria are:

date Sort the messages by their ‘Date:’ field, that is by the time they
were sent.
from Sort messages by the value of their ‘From:’ field, that is by the
address of the sender. If the showname variable is set, the
sender's real name (if any) is used.
size Sort the messages by their size.
spam [Option] Sort the message by their spam score, as has been
classified by spamrate.
status Sort the messages by their message status.
subject Sort the messages by their subject.
thread Create a threaded display.
to Sort messages by the value of their ‘To:’ field, that is by the
address of the recipient. If the showname variable is set, the
recipient's real name (if any) is used.

If no argument is given, the current sorting criterion is printed.

source (so) The source command reads commands from a file.

source_if
The difference to source is that this command will not generate an error if the
given file argument cannot be opened successfully. This can matter in, e.g.,
resource files, since loading of those is stopped when an error is encountered.

spamclear
[Option] Takes a list of messages and clears their ‘is-spam’ flag.

spamforget
[Option] Takes a list of messages and causes the spam-interface to forget it has
ever used them to train its Bayesian filter. Unless otherwise noted the ‘is-spam’
flag of the message is inspected to chose wether a message shall be forgotten to be
“ham” or “spam”.

spamham [Option] Takes a list of messages and informs the Bayesian filter of the
spam-interface that they are “ham”. This also clears the ‘is-spam’ flag of the
messages in question.

spamrate
[Option] Takes a list of messages and rates them using the configured
spam-interface, without modifying the messages, but setting their ‘is-spam’ flag as
appropriate; because the spam rating headers are lost the rate will be forgotten
once the mailbox is left. Refer to the manual section Handling spam for the
complete picture of spam handling in S-nail.

spamset [Option] Takes a list of messages and sets their ‘is-spam’ flag.

spamspam
[Option] Takes a list of messages and informs the Bayesian filter of the
spam-interface that they are “spam”. This also sets the ‘is-spam’ flag of the
messages in question.

thread [Obsolete] The same as ‘sort thread’ (consider using a ‘ghost’ as necessary).
Create a threaded representation of the current folder, i.e. indent messages that
are replies to other messages in the header display and change the next command and
the addressing modes such that they refer to messages in the threaded order.
Message numbers are the same as in unthreaded mode. If the header variable is set,
a header summary in threaded order is also printed.

top (to) Takes a message list and prints the top few lines of each. The number of
lines printed is controlled by the variable toplines and defaults to five.

touch (tou) Takes a message list and marks the messages for saving in MBOX. S-nail
deviates from the POSIX standard with this command, as a following next command
will display the following message instead of the current one.

Type (T) Identical to the Print command.

type (t) A synonym for print.

unaccount
Delete all given accounts. An error message is printed if a given account is not
defined. The special name ‘*’ will discard all existing accounts.

unalias (una) Takes a list of names defined by alias commands and discards the remembered
groups of users. The special name ‘*’ will discard all existing aliases.

unanswered
Takes a message list and marks each message as not having been answered.

uncollapse
Only applicable to threaded mode. Takes a message list and makes the message and
all replies to it visible in header summaries again. When a message becomes the
current message, it is automatically made visible. Also when a message with
collapsed replies is printed, all of these are automatically uncollapsed.

undefine
Undefine all given macros. An error message is printed if a given macro is not
defined. The special name ‘*’ will discard all existing macros.

undelete
(u) Takes a message list and marks each message as not being deleted.

undraft Takes a message list and undrafts each message.

unflag Takes a message list and marks each message as not being flagged.

unfwdignore
Removes the header field names from the list of ignored fields for the forward
command. The special name ‘*’ will remove all fields.

unfwdretain
Removes the header field names from the list of retained fields for the forward
command. The special name ‘*’ will remove all fields.

unghost Remove all the given command ghosts. The special name ‘*’ will remove all ghosts.

unignore
Removes the header field names from the list of ignored fields. The special name
‘*’ will remove all fields.

unmimetype
Delete all given MIME types, e.g., ‘unmimetype text/plain’ will remove all
registered specifications for the MIME type ‘text/plain’. The special name ‘*’
will discard all existing MIME types, just as will ‘reset’, but which also
reenables cache initialization via mimetypes-load-control.

unmlist Forget about all the given mailing lists. The special name ‘*’ will remove all
lists. Also see mlist.

unmlsubscribe
Remove the subscription attribute from all given mailing lists. The special name
‘*’ will clear the attribute from all lists which have it set. Also see
mlsubscribe.

Unread Same as unread.

unread Takes a message list and marks each message as not having been read.

unretain
Removes the header field names from the list of retained fields. The special name
‘*’ will remove all fields.

unsaveignore
Removes the header field names from the list of ignored fields for saving. The
special name ‘*’ will remove all fields.

unsaveretain
Removes the header field names from the list of retained fields for saving. The
special name ‘*’ will remove all fields.

unset (uns) Takes a list of option names and discards their remembered values; the
inverse of set.

unsetenv
Identical to unset except that the options are also removed from the program
environment; since this task requires native host support the command will always
report error if that is not available (but still act like unset). This operation
is a no-op unless all resource files have been loaded. Also see setenv.

unshortcut
Deletes the shortcut names given as arguments. The special name ‘*’ will remove
all shortcuts.

unsort Disable sorted or threaded mode (see the sort and thread commands), return to
normal message order and, if the header variable is set, print a header summary.

unthread
[Obsolete] Same as unsort.

urldecode
Decode the given URL-encoded string arguments and show the results.

urlencode
URL-encode the given arguments and show the results.

varedit Edit the values of or create the given variable(s) in the EDITOR. Binary variables
cannot be edited.

varshow Show informations about all the given options. S-nail knows about a finite set of
known builtin variables that are subdivided further in binary and value variants;
they may have special properties, like “read-only” (setting may not be changed) and
“virtual”, meaning that the value is generated on-the-fly as necessary. Beside
those known variables an infinite number of unknown, so-called “assembled”
variables, which are expected to be able to store values, may exist.

? set foo=bar nobar
? varshow sendwait version-major foo bar
"sendwait": (73) binary: set=1 (ENVIRON=0)
"version-major": (192) value, read-only, virtual:\
set=1 (ENVIRON=0) value<14>
"foo": (assembled) set=1 (ENVIRON=0) value<bar>
"bar": (assembled) set=0 (ENVIRON=0) value<NULL>

verify [Option] Takes a message list and verifies each message. If a message is not a
S/MIME signed message, verification will fail for it. The verification process
checks if the message was signed using a valid certificate, if the message sender's
email address matches one of those contained within the certificate, and if the
message content has been altered.

visual (v) Takes a message list and invokes the display editor on each message. Modified
contents are discarded unless the writebackedited variable is set.

write (w) For conventional messages the body without all headers is written. The output
is decrypted and converted to its native format as necessary. If the output file
exists, the text is appended. If a message is in MIME multipart format its first
part is written to the specified file as for conventional messages, and the user is
asked for a filename to save each other part. For convience saving of each part
may be skipped by giving an empty value; the same result can also be achieved by
writing it to /dev/null. For the second and subsequent parts a leading ‘|’
character causes the part to be piped to the remainder of the user input
interpreted as a shell command; otherwise the user input is expanded as usually for
folders, e.g., tilde expansion is performed. In non-interactive mode, only the
parts of the multipart message that have a filename given in the part header are
written, the others are discarded. The original message is never marked for
deletion in the originating mail folder. For attachments, the contents of the
destination file are overwritten if the file previously existed. No special
handling of compressed files is performed.

xit (x) A synonym for exit.

z S-nail presents message headers in windowfuls as described under the headers
command. This command scrolls to the next window of messages. If an argument is
given, it specifies the window to use. A number prefixed by ‘+’ or ‘-’ indicates
that the window is calculated in relation to the current position. A number
without a prefix specifies an absolute window number, and a ‘$’ lets S-nail scroll
to the last window of messages.

Z Similar to z, but scrolls to the next or previous window that contains at least one
‘new’ or flagged message.

TILDE ESCAPES


Here is a summary of the tilde escapes, which are used to perform special functions when
composing messages. Tilde escapes are only recognized at the beginning of lines. The name
“tilde escape” is somewhat of a misnomer since the actual escape character can be changed by
adjusting the option escape.

~~ string Insert the string of text in the message prefaced by a single ‘~’. (If the
escape character has been changed, that character must be doubled in order to
send it at the beginning of a line.)

~! command Execute the indicated shell command, then return to the message.

~. Same effect as typing the end-of-file character.

~: S-nail-command or ~_ S-nail-command
Execute the given S-nail command. Not all commands, however, are allowed.

~? Write a summary of command escapes.

~< filename Identical to ~r.

~<! command command is executed using the shell. Its standard output is inserted into the
message.

~@ [filename...]
With no arguments, edit the attachment list interactively. If an attachment's
file name is left empty, that attachment is deleted from the list. When the
end of the attachment list is reached, S-nail will ask for further attachments
until an empty name is given. If a given file name solely consists of the
number sign ‘#’ followed by a valid message number of the currently active
mailbox, then the given message is attached as a MIME ‘message/rfc822’ and the
rest of this section does not apply.

If character set conversion has been compiled into S-nail, then this mode gives
the user the option to specify input and output character sets, unless the file
extension indicates binary content, in which case S-nail asks wether this step
shall be skipped for the attachment in question. If not skipped, then the
charset that succeeds to represent the attachment data will be used in the
‘charset=’ MIME parameter of the mail message:

· If input and output character sets are specified, then the conversion is
performed on the fly. The user will be asked repeatedly until the desired
conversion succeeds.
· If only an output character set is specified, then the input is assumed to
be in the ttycharset charset and will be converted to the given output
charset on the fly. The user will be asked repeatedly until the desired
conversion succeeds.
· If no character sets are specified at all then the algorithm that is
documented in the section Character sets is applied, but directly and on
the fly. The user will be asked repeatedly until the desired conversion
succeeds.
· Finally, if an input-, but no output character set is specified, then no
conversion is ever performed, but the ‘charset=’ MIME parameter value will
still be set to the user input.
· The character set selection loop can be left by typing ‘control-C’, i.e.,
causing an interrupt. Note that before S-nail version 15.0 this terminates
the entire current attachment selection, not only the character set
selection.

Without character set conversion support, S-nail will ask for the input
character set only, and it'll set the ‘charset=’ MIME parameter value to the
given input, if any; if no user input is seen then the ttycharset character set
will be used for the parameter value instead. Note that the file extension
check isn't performed in this mode, since no conversion will take place anyway.

Note that in non-interactive mode, for reproduceabilities sake, there will
always be two questions for each attachment, regardless of wether character set
conversion is available and what the file extension is. The first asks for the
filename, and the second asks for the input character set to be passed through
to the corresponding MIME parameter; no conversion will be tried if there is
input to the latter question, otherwise the usual conversion algorithm, as
above, is applied. For message attachments, the answer to the second question
is completely ignored.

If (instead) filename arguments are specified for the ~@ command they are
treated as a comma separated list of files, which are all expanded and appended
to the end of the attachment list. (Filenames with commas, or with leading or
trailing whitespace can only be added via the command line or the first method.
Message attachments can only be added via the first method; filenames which
clash with message numbers can only be added via the command line or the second
method.) In this mode the (text) attachments are assumed to be in ttycharset
encoding, and will be evaluated as documented in the section Character sets.

~A Inserts the string contained in the Sign variable (same as ‘~i Sign’). The
escape sequences tabulator ‘\t’ and newline ‘\n’ are understood.

~a Inserts the string contained in the sign variable (same as ‘~i sign’). The
escape sequences tabulator ‘\t’ and newline ‘\n’ are understood.

~b name ... Add the given names to the list of blind carbon copy recipients.

~c name ... Add the given names to the list of carbon copy recipients.

~d Read the file specified by the DEAD variable into the message.

~e Invoke the text editor on the message collected so far. After the editing
session is finished, the user may continue appending text to the message.

~F messages Read the named messages into the message being sent, including all message
headers and MIME parts. If no messages are specified, read in the current
message.

~f messages Read the named messages into the message being sent. If no messages are
specified, read in the current message. ignore and retain lists are used to
modify the message headers. For MIME multipart messages, only the first
printable part is included.

~H Edit the message header fields ‘From:’, ‘Reply-To:’, ‘Sender:’ and
‘Organization:’ by typing each one in turn and allowing the user to edit the
field. The default values for these fields originate from the from, replyto,
sender and ORGANIZATION variables.

~h Edit the message header fields ‘To:’, ‘Cc:’, ‘Bcc:’ and ‘Subject:’ by typing
each one in turn and allowing the user to edit the field.

~i variable Insert the value of the specified variable into the message, adding a newline
character at the end. The message remains unaltered if the variable is unset
or empty. The escape sequences tabulator ‘\t’ and newline ‘\n’ are understood.

~M messages Read the named messages into the message being sent, indented by indentprefix.
If no messages are specified, read the current message.

~m messages Read the named messages into the message being sent, indented by indentprefix.
If no messages are specified, read the current message. ignore and retain
lists are used to modify the message headers. For MIME multipart messages,
only the first printable part is included.

~p Print out the message collected so far, prefaced by the message header fields
and followed by the attachment list, if any.

~q Abort the message being sent, copying it to the file specified by the DEAD
variable if save is set.

~R filename Read the named file into the message, indented by indentprefix.

~r filename Read the named file into the message.

~s string Cause the named string to become the current subject field.

~t name ... Add the given name(s) to the direct recipient list.

~U messages Read in the given / current message(s) excluding all headers, indented by
indentprefix.

~u messages Read in the given / current message(s), excluding all headers.

~v Invoke an alternate editor (defined by the VISUAL option) on the message
collected so far. Usually, the alternate editor will be a screen editor.
After the editor is quit, the user may resume appending text to the end of the
message.

~w filename Write the message onto the named file. If the file exists, the message is
appended to it.

~x Same as ~q, except that the message is not saved at all.

~| command Pipe the message through the specified filter command. If the command gives no
output or terminates abnormally, retain the original text of the message.
E.g., the command fmt(1) is often used as a rejustifying filter.

VARIABLE OPTIONS


Variables are controlled via set and unset commands; in general using unset can also be
accomplished by prefixing a variable name with the string “no” and calling set, e.g., ‘unset
crt’ will have the same effect as ‘set nocrt’. Creation or editing of variables in an
editor can also be achieved with varedit. varshow will give more insight on the given
variable(s), whereas set will print a listing of all variables when called without
arguments. Options are also implicitly inherited from the program ENVIRONMENT and can be
set explicitly via the command line option -S.

Different kind of options exist: binary options, which can only be in one of the two states
“set” and “unset”, as well as value options which have an assigned string value, for which
proper quoting may be important upon assignment time.

Initial Settings
The standard POSIX 2008/Cor 1-2013 mandates the following initial variable settings:
noallnet, noappend, asksub, noaskbcc, noautoprint, nobang, nocmd, nocrt, nodebug, nodot,
escape set to ‘~’, noflipr, nofolder, header, nohold, noignore, noignoreeof, nokeep,
nokeepsave, nometoo, nooutfolder, nopage, prompt set to ‘? ’ (note that S-nail deviates from
the standard by using ‘\& ’, but the ‘\&’ special prompt escape results in “?” being printed
unless bsdcompat is set), noquiet, norecord, save, nosendwait, noshowto, noSign, nosign,
toplines set to ‘5’.

Notes: S-nail doesn't support the noonehop variable – use command line options or
sendmail-arguments to pass options through to a MTA. And the default global s-nail.rc file
(which is loaded unless the -n command line flag has been used or the NAIL_NO_SYSTEM_RC
environment variable is set) bends those initial settings a bit, e.g., it sets the options
hold, keepsave and keep, to name a few, calls retain etc., and should thus be taken into
account.

Binary options
add-file-recipients
When file or pipe recipients have been specified, mention them in the
corresponding address fields of the message instead of silently stripping them
from their recipient list. By default such addressees are not mentioned.

allnet Causes only the local part to be evaluated when comparing addresses.

append Causes messages saved in MBOX to be appended to the end rather than prepended.
This should always be set.

ask or asksub
Causes S-nail to prompt for the subject of each message sent. If the user
responds with simply a newline, no subject field will be sent.

askatend Causes the prompts for ‘Cc:’ and ‘Bcc:’ lists to appear after the message has
been edited.

askattach If set, S-nail asks for files to attach at the end of each message, shall the
list be found empty at that time. An empty line finalizes the list.

askcc Causes the user to be prompted for carbon copy recipients (at the end of each
message if askatend or bsdcompat are set) shall the list be found empty (at that
time). An empty line finalizes the list.

askbcc Causes the user to be prompted for blind carbon copy recipients (at the end of
each message if askatend or bsdcompat are set) shall the list be found empty (at
that time). An empty line finalizes the list.

asksign [Option] Causes the user to be prompted if the message is to be signed at the end
of each message. The smime-sign variable is ignored when this variable is set.

autocollapse
Causes threads to be collapsed automatically when threaded mode is entered (see
the collapse command).

autoprint Causes the delete command to behave like ‘dp -’; thus, after deleting a message
the next one will be typed automatically.

autothread
[Obsolete] Causes threaded mode (see the thread command) to be entered
automatically when a folder is opened. The same as ‘autosort=thread’.

bang Enables the substitution of ‘!’ by the contents of the last command line in shell
escapes.

batch-exit-on-error
If the batch mode has been enabled via the -# command line option, then this
variable will be consulted whenever S-nail completes one operation (returns to
the command prompt); if it is set then S-nail will terminate if the last
operation generated an error.

bsdannounce
Causes automatic display of a header summary after executing a file command.

bsdcompat Sets some cosmetical features to traditional BSD style; has the same affect as
setting askatend and all other variables prefixed with ‘bsd’; it also changes the
meaning of the S-nail specific ‘\&’ prompt escape sequence.

bsdflags Changes the letters printed in the first column of a header summary to
traditional BSD style.

bsdheadline
Changes the display of columns in a header summary to traditional BSD style.

bsdmsgs Changes some informational messages to traditional BSD style.

bsdorder Causes the ‘Subject:’ field to appear immediately after the ‘To:’ field in
message headers and with the ~h TILDE ESCAPES.

bsdset Changes the output format of the set command to traditional BSD style.

colour-disable
[Option] Forcefully disable usage of colours. Also see the section Coloured
message display.

colour-pager
[Option] Wether colour shall be used for output that is paged through PAGER.
Note that pagers may need special flags, e.g., less(1) requires the option -R and
lv(1) the option -c in order to support colours; therefore S-nail will inspect
the variable PAGER – if that starts with the string “less” a non-existing
environment variable LESS will be set to ‘FRSXi’, likewise for “lv” LV will
optionally be set to “-c”. Also see the section Coloured message display for
more on this.

debug Prints debugging messages and disables the actual delivery of messages. Also
implies norecord and nosave.

disconnected
[Option] When an IMAP mailbox is selected and this variable is set, no connection
to the server is initiated. Instead, data is obtained from the local cache (see
imap-cache). Mailboxes that are not present in the cache and messages that have
not yet entirely been fetched from the server are not available; to fetch all
messages in a mailbox at once, the command `copy * /dev/null' can be used while
still in connected mode. Changes that are made to IMAP mailboxes in disconnected
mode are queued and committed later when a connection to that server is made.
This procedure is not completely reliable since it cannot be guaranteed that the
IMAP unique identifiers (UIDs) on the server still match the ones in the cache at
that time. Data is saved to DEAD when this problem occurs.

disconnected-USER@HOST
The specified account is handled as described for the disconnected variable
above, but other accounts are not affected.

disposition-notification-send
[Option] Emit a ‘Disposition-Notification-To:’ header (RFC 3798) with the
message. This requires a set from variable.

dot When dot is set, a dot ‘.’ on a line by itself during message input from a
terminal shall be treated as end-of-message (in addition to the normal end-of-
file condition). If ignoreeof is set nodot is ignored and using a dot is the
only method to terminate input mode.

dotlock-ignore-error
[Option] Synchronization of mailboxes which S-nail treats as system mailboxes
(see the command file) will be protected with so-called dotlock files—the
traditional mail spool file locking method—in addition to system file locking.
Because S-nail ships with a privilege-separated dotlock creation program that
should always be able to create such a dotlock file there is no good reason to
ignore dotlock file creation errors, and thus these are fatal unless this
variable is set.

editalong If this variable is set then the editor is started automatically when a message
is composed in interactive mode, as if the ~e TILDE ESCAPES had been specified.
The editheaders variable is implied for this automatically spawned editor
session.

editheaders
When a message is edited while being composed, its header is included in the
editable text. The ‘To:’, ‘Cc:’, ‘Bcc:’, ‘Subject:’, ‘From:’, ‘Reply-To:’,
‘Sender:’, and ‘Organization:’ fields are accepted within the header, other
fields are ignored.

emptystart
If the mailbox is empty S-nail normally prints “No mail for user” and exits
immediately. If this option is set S-nail starts even with an empty mailbox.

flipr This option reverses the meanings of a set of reply commands, turning the
lowercase variants, which by default address all recipients included in the
header of a message (reply, respond, followup) into the uppercase variants, which
by default address the sender only (Reply, Respond, Followup) and vice versa.
The commands replysender, respondsender, followupsender as well as replyall,
respondall, followupall are not affected by the current setting of flipr.

followup-to
Controls wether a ‘Mail-Followup-To:’ header is generated when sending messages
to known mailing lists. Also see followup-to-honour and the commands mlist,
mlsubscribe, reply and Lreply.

forward-as-attachment
Original messages are normally sent as inline text with the forward command, and
only the first part of a multipart message is included. With this option
messages are sent as unmodified MIME ‘message/rfc822’ attachments with all of
their parts included.

fullnames When replying to or forwarding a message S-nail normally removes the comment and
name parts of email addresses. If this variable is set such stripping is not
performed, and comments, names etc. are retained.

header Causes the header summary to be written at startup and after commands that affect
the number of messages or the order of messages in the current folder; enabled by
default. The command line option -N can be used to set noheader.

history-gabby
[Option] Add more entries to the history as is normally done.

history-gabby-persist
[Option] S-nails own NCL will not save the additional (gabby) history entries in
persistent storage unless this variable is also set. Also see NAIL_HISTFILE.

hold This option is used to hold messages in the system mailbox by default.

idna-disable
[Option] Can be used to turn off the automatic conversion of domain names
according to the rules of IDNA (internationalized domain names for applications).
Since the IDNA code assumes that domain names are specified with the ttycharset
character set, an UTF-8 locale charset is required to represent all possible
international domain names (before conversion, that is).

ignore Ignore interrupt signals from the terminal while entering messages; instead echo
them as ‘@’ characters and discard the current line.

ignoreeof Ignore end-of-file conditions (‘control-D’), on message input, which instead can
be terminated only by entering a dot ‘.’ on a line by itself or by using the ~.
TILDE ESCAPES. This option also applies to S-nail command mode.

imap-use-starttls-USER@HOST, imap-use-starttls-HOST, imap-use-starttls
[Option] Causes S-nail to issue a `STARTTLS' command to make an unencrypted IMAP
session SSL/TLS encrypted. This functionality is not supported by all servers,
and is not used if the session is already encrypted by the IMAPS method.

keep If set, an empty mailbox file is not removed. This may improve the
interoperability with other mail user agents when using a common folder
directory, and prevents malicious users from creating fake mailboxes in a world-
writable spool directory. Note this only applies to local regular (MBOX) files,
other mailbox types will never be removed.

keepsave When a message is saved it is usually discarded from the originating folder when
S-nail is quit. Setting this option causes all saved message to be retained.

line-editor-disable
Turn off any enhanced command line editing capabilities (see Command line editor
for more).

markanswered
When a message is replied to and this variable is set, it is marked as having
been answered. This mark has no technical meaning in the mail system; it just
causes messages to be marked in the header summary, and makes them specially
addressable.

mbox-rfc4155
S-nail produces and expects fully RFC 4155 compliant MBOX text mailboxes.
Messages which are fetched over the network or from within already existing
Maildir (or any non-MBOX) mailboxes may require so-called ‘From_’ quoting
(insertion of additional ‘>’ characters to prevent line content
misinterpretation) to be applied in order to be storable in MBOX mailboxes,
however, dependent on the circumspection of the message producer. (E.g., S-nail
itself will, when newly generating messages, choose a Content-Transfer-encoding
that prevents the necessity for such quoting – a necessary precondition to ensure
message checksums won't change.)

By default S-nail will perform this ‘From_’ quoting in a way that results in a
MBOX file that is compatible with the loose POSIX MBOX layout, in order not to
exceed the capabilities of simple applications, however. Set this option to
generate MBOX files for RFC 4155 compliant applications only.

message-id-disable
By setting this option the generation of ‘Message-ID:’ can be completely
suppressed, effectively leaving this task up to the mail-transfer-agent (MTA) or
the SMTP server. (According to RFC 5321 your SMTP server is not required to add
this field by itself, so you should ensure that it accepts messages without a
‘Message-ID’.)

metoo Usually, when an alias expansion contains the sender, the sender is removed from
the expansion. Setting this option suppresses these removals. Note that a set
metoo also causes a ‘-m’ option to be passed to mail-transfer-agents (MTAs);
though most of the modern MTAs don't (no longer) document this flag, no MTA is
known which doesn't support it (for historical compatibility).

mime-allow-text-controls
When sending messages, each part of the message is MIME-inspected in order to
classify the ‘Content-Type:’ and ‘Content-Transfer-Encoding:’ (see encoding) that
is required to send this part over mail transport, i.e., a computation rather
similar to what the file(1) command produces when used with the ‘--mime’ option.

This classification however treats text files which are encoded in UTF-16 (seen
for HTML files) and similar character sets as binary octet-streams, forcefully
changing any ‘text/plain’ or ‘text/html’ specification to
‘application/octet-stream’: If that actually happens a yet unset charset MIME
parameter is set to ‘binary’, effectively making it impossible for the receiving
MUA to automatically interpret the contents of the part.

If this option is set, and the data was unambiguously identified as text data at
first glance (by a ‘.txt’ or ‘.html’ file extension), then the original
‘Content-Type:’ will not be overwritten.

netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup
[v15-compat] [Option] Used to control usage of the users .netrc file for lookup
of account credentials, as documented in the section On URL syntax and credential
lookup and for the command netrc; the section The .netrc file documents the file
format.

outfolder Causes the filename given in the record variable and the sender-based filenames
for the Copy and Save commands to be interpreted relative to the directory given
in the folder variable rather than to the current directory, unless it is set to
an absolute pathname.

page If set, each message the pipe command prints out is followed by a formfeed
character ‘\f’.

piperaw Send messages to the pipe command without performing MIME and character set
conversions.

pop3-bulk-load-USER@HOST, pop3-bulk-load-HOST, pop3-bulk-load
[Option] When accessing a POP3 server S-nail loads the headers of the messages,
and only requests the message bodies on user request. For the POP3 protocol this
means that the message headers will be downloaded twice. If this option is set
then S-nail will download only complete messages from the given POP3 server(s)
instead.

pop3-no-apop-USER@HOST, pop3-no-apop-HOST, pop3-no-apop
[Option] Unless this variable is set the ‘APOP’ authentication method will be
used when connecting to a POP3 server that advertises support. The advantage of
‘APOP’ is that the password is not sent in clear text over the wire and that only
a single packet is sent for the user/password tuple. Note that pop3-no-apop-HOST
requires [v15-compat].

pop3-use-starttls-USER@HOST, pop3-use-starttls-HOST, pop3-use-starttls
[Option] Causes S-nail to issue a ‘STLS’ command to make an unencrypted POP3
session SSL/TLS encrypted. This functionality is not supported by all servers,
and is not used if the session is already encrypted by the POP3S method. Note
that pop3-use-starttls-HOST requires [v15-compat].

print-all-chars
This option causes all characters to be considered printable. It is only
effective if given in a startup file. With this option set some character
sequences in messages may put the user's terminal in an undefined state when
printed; it should only be used as a last resort if no working system locale can
be found.

print-alternatives
When a MIME message part of type ‘multipart/alternative’ is displayed and it
contains a subpart of type ‘text/plain’, other parts are normally discarded.
Setting this variable causes all subparts to be displayed, just as if the
surrounding part was of type ‘multipart/mixed’.

quiet Suppresses the printing of the version when first invoked.

quote-as-attachment
If this is set, then the original message is added in its entirety as a
‘message/rfc822’ MIME attachment when replying to a message. Note this works
regardless of the setting of quote.

recipients-in-cc
On group replies, specify only the sender of the original mail in ‘To:’ and
mention the other recipients in the secondary ‘Cc:’. By default all recipients
of the original mail will be addressed via ‘To:’.

record-resent
If both this variable and the record variable are set, the resend and Resend
commands save messages to the record folder as it is normally only done for newly
composed messages.

reply-in-same-charset
If this variable is set S-nail first tries to use the same character set of the
original message for replies. If this fails, the mechanism described in
Character sets is evaluated as usual.

rfc822-body-from_
This variable can be used to force displaying a so-called ‘From_’ line for
messages that are embedded into an envelope mail via the ‘message/rfc822’ MIME
mechanism, for more visual convenience.

save Enable saving of (partial) messages in DEAD upon interrupt or delivery error.

searchheaders
Expand message-list specifiers in the form ‘/x:y’ to all messages containing the
substring “y” in the header field ‘x’. The string search is case insensitive.

sendcharsets-else-ttycharset
[Option] If this variable is set, but sendcharsets is not, then S-nail acts as if
sendcharsets had been set to the value of the variable ttycharset. In effect
this combination passes through the message data in the character set of the
current locale (given that ttycharset hasn't been set manually), i.e., without
converting it to the charset-8bit fallback character set. Thus, mail message
text will be in ISO-8859-1 encoding when send from within a ISO-8859-1 locale,
and in UTF-8 encoding when send from within an UTF-8 locale. If no character set
conversion capabilities are available in S-nail then the only supported character
set is ttycharset.

sendmail-no-default-arguments
Unless this option is set S-nail will pass some well known standard command line
options to the defined sendmail program, see there for more.

sendwait When sending a message wait until the MTA (including the builtin SMTP one) exits
before accepting further commands. Only with this variable set errors reported
by the MTA will be recognizable! If the MTA returns a non-zero exit status, the
exit status of s-nail will also be non-zero.

showlast Setting this option causes S-nail to start at the last message instead of the
first one when opening a mail folder.

showname Causes S-nail to use the sender's real name instead of the plain address in the
header field summary and in message specifications.

showto Causes the recipient of the message to be shown in the header summary if the
message was sent by the user.

skipemptybody
If an outgoing message does not contain any text in its first or only message
part, do not send it but discard it silently (see also the command line option
-E).

smime-force-encryption
[Option] Causes S-nail to refuse sending unencrypted messages.

smime-sign
[Option] S/MIME sign outgoing messages with the user's private key and include
the user's certificate as a MIME attachment. Signing a message enables a
recipient to verify that the sender used a valid certificate, that the email
addresses in the certificate match those in the message header and that the
message content has not been altered. It does not change the message text, and
people will be able to read the message as usual. Also see smime-sign-cert,
smime-sign-include-certs and smime-sign-message-digest.

smime-no-default-ca
[Option] Don't load default CA locations when verifying S/MIME signed messages.

smtp-use-starttls-USER@HOST, smtp-use-starttls-HOST, smtp-use-starttls
[Option] Causes S-nail to issue a ‘STARTTLS’ command to make an SMTP session
SSL/TLS encrypted, i.e., to enable transport layer security.

ssl-no-default-ca
[Option] Don't load default CA locations to verify SSL/TLS server certificates.

term-ca-mode
[Option] If terminal capability queries are supported and this option is set then
S-nail will try to switch to the “alternate screen” when in interactive mode, so
that the terminal will go back to the normal screen, leaving all the text there
intact, when S-nail exits. Note: even when supported for this to produce
appealing results the used PAGER and possibly configured pipe-TYPE/SUBTYPE
applications that take control over the terminal need to have corresponding
support too, e.g., the less(1) pager should be driven with the ‘-X’ command line
flag.

keep-content-length
When (editing messages and) writing MBOX mailbox files S-nail can be told to keep
the ‘Content-Length:’ and ‘Lines:’ header fields that some MUAs generate by
setting this variable. Since S-nail does neither use nor update these non-
standardized header fields (which in itself shows one of their conceptual
problems), stripping them should increase interoperability in between MUAs that
work with with same mailbox files. Note that, if this is not set but
writebackedited, as below, is, a possibly performed automatic stripping of these
header fields already marks the message as being modified.

v15-compat
Setting this option enables upward compatibility with S-nail version 15.0 in
respect to which configuration options are available and how they are handled.
This manual uses [v15-compat] and [no v15-compat] to refer to the new and the old
way of doing things, respectively.

verbose Setting this option, also controllable via the command line option -v, causes
S-nail to be more verbose, so that, e.g., certificate chains will be displayed on
the users terminal. Setting this binary option twice increases the level of
verbosity, in which case even details of the actual message delivery and protocol
conversations are shown. A single noverbose is sufficient to disable verbosity
as such.

writebackedited
If this variable is set messages modified using the edit or visual commands are
written back to the current folder when it is quit; it is only honoured for
writable folders in MBOX format, though. Note that the editor will be pointed to
the raw message content in that case, i.e., neither MIME decoding nor decryption
will have been performed, and proper RFC 4155 ‘From_’ quoting of newly added or
edited content is also left as an excercise to the user.

Value options
Options with values that are generally treated as strings. To embed whitespace (space and
tabulator) in a value it either needs to be escaped with a backslash character, or the
entire value must be enclosed in (double or single) quotation marks; To use quotation marks
identical to those used to enclose the value, escape them with a backslash character. The
backslash character has no special meaning except in these cases.

set 1=val\ one 2="val two" 3='val "three"' 4='val \'four\''
varshow 1 2 3 4
unset 1 2 3 4

Booleans are special string values that must either be set to decimal integers (in which
case ‘0’ is false and ‘1’ and any other value is true) or to any of ‘off’, ‘no’ and ‘false’
for a false boolean and ‘on’, ‘yes’ and ‘true’ for a true boolean; matching is performed
case-insensitively. And there exists a special kind of boolean, the “quadoption”: this is
expected to either name a boolean or one of the strings ‘ask-yes’ and ‘ask-no’ (in fact:
‘ask-’ followed by a valid boolean, case-insensitively); if one of the latter is set then in
interactive mode the user will be prompted with the default value (also used for empty user
input) set to the given boolean, whereas in non-interactive the given default will be used
right away.

agent-shell-lookup-USER@HOST, agent-shell-lookup-HOST, agent-shell-lookup
[v15-compat] [Option] Account passwords can be fetched via an external agent
program in order to permit encrypted password storage – see On URL syntax and
credential lookup for more on credential lookup. If this is set then the content
is interpreted as a shell command the output of which (with newline characters
removed) is treated as the account password shall the command succeed (and have
produced non-empty non-newline output); e.g., via gpg(1):

$ echo PASSWORD > .pass
$ gpg -e .pass
$ eval `gpg-agent --daemon \
--pinentry-program=/usr/bin/pinentry-curses \
--max-cache-ttl 99999 --default-cache-ttl 99999`
$ echo 'set agent-shell-lookup="gpg -d .pass.gpg"' \
>> ~/.mailrc

A couple of environment variables will be set for the agent:

NAIL_TMPDIR The temporary directory that S-nail uses. Usually identical to
TMPDIR, but guaranteed to be set and usable by child processes;
to ensure the latter condition for TMPDIR also, it'll be set.
NAIL_USER The user (‘USER’) for which the password is looked up.
NAIL_USER_ENC The URL percent-encoded variant of NAIL_USER.
NAIL_HOST The plain machine hostname of the user account.
NAIL_HOST_PORT The ‘HOST’ (hostname possibly including port) of the user
account.

attrlist A sequence of characters to print in the ‘attribute’ column of the headline as
shown in the header display; each for one type of messages (see Message states),
with the default being ‘NUROSPMFAT+-$~’ or ‘NU *HMFAT+-$~’ if bsdflags or the
SYSV3 environment variable are set, in the following order:

‘N’ new.
‘U’ unread but old.
‘R’ new but read.
‘O’ read and old.
‘S’ saved.
‘P’ preserved.
‘M’ mboxed.
‘F’ flagged.
‘A’ answered.
‘T’ draft.
‘+’ start of a collapsed thread.
‘-’ collapsed.
‘$’ classified as spam.
‘~’ classified as possible spam.

autobcc Specifies a list of recipients to which a blind carbon copy of each outgoing
message will be sent automatically.

autocc Specifies a list of recipients to which a carbon copy of each outgoing message
will be sent automatically.

autosort Causes sorted mode (see the sort command) to be entered automatically with the
value of this option as sorting method when a folder is opened.

charset-7bit
The value that should appear in the ‘charset=’ parameter of ‘Content-Type:’ MIME
header fields when no character set conversion of the message data was performed.
This defaults to US-ASCII, and the chosen character set should be US-ASCII
compatible.

charset-8bit
[Option] The default 8-bit character set that is used as an implicit last member
of the variable sendcharsets. This defaults to UTF-8. If no character set
conversion capabilities are available in S-nail then the only supported character
set is ttycharset. Refer to the section Character sets for the complete picture
of character set conversion in S-nail.

charset-unknown-8bit
[Option] RFC 1428 specifies conditions when internet mail gateways shall
“upgrade” the content of a mail message by using a character set with the name
‘unknown-8bit’. Because of the unclassified nature of this character set S-nail
will not be capable to convert this character set to any other character set. If
this variable is set any message part which uses the character set ‘unknown-8bit’
is assumed to really be in the character set given in the value, otherwise the
(final) value of charset-8bit is used for this purpose.

cmd The default value for the pipe command.

colour-from_
[Option] The colour specification for so-called ‘From_’ lines. See the section
Coloured message display for the format of the value.

colour-header
[Option] The colour specification for header lines.

colour-msginfo
[Option] The colour specification for the introductional message info line.

colour-partinfo
[Option] The colour specification for MIME part info lines.

colour-terms
[Option] A comma-separated list of TERMinals for which coloured message display
can be used. Entries only need to be added if the string “color” isn't part of
the terminal name itself; the default value is

cons25,linux,rxvt,rxvt-unicode,screen,sun,vt100,vt220,wsvt25,xterm

colour-uheader
[Option] The colour specification for those header lines that have been placed in
the colour-user-headers list. See the section Coloured message display.

colour-user-headers
A comma separated list of (case-insensitive) header names which should be
colourized with the alternative colour-uheader colours. The default value is
‘from,subject’.

crt In a(n interactive) terminal session, then if this valued option is set it'll be
used as a threshold to determine how many lines the given output has to span
before it will be displayed via the configured PAGER; Usage of the PAGER can be
forced by setting this to the value ‘0’, setting it without a value will deduce
the current height of the terminal screen to compute the treshold (see LINES and
stty(1)).

datefield The date in a header summary is normally the date of the mailbox ‘From_’ line of
the message. If this variable is set, then the date as given in the ‘Date:’
field is used, converted to local time. It is possible to control the display of
the date by assigning a value, in which case the strftime(3) function will be
used to format the date accordingly. Please read your system manual for the
available formats. Note that the ‘%n’ format should not be used, because S-nail
doesn't take embedded newlines into account when calculating how many lines fit
onto the screen.

datefield-markout-older
This option, when set in addition to datefield, is used to display “older”
messages (concept is rather comparable to the -l option of the POSIX utility
ls(1)). The content interpretation is identical to datefield.

encoding Suggestion for the MIME encoding to use in outgoing text messages and message
parts. Valid values are the default ‘quoted-printable’, ‘8bit’ and ‘base64’.
‘8bit’ may cause problems when transferring mail messages over channels that are
not ESMTP (RFC 1869) compliant. If there is no need to encode a message, ‘7bit’
transfer mode is always used regardless of this variable. Binary data is always
encoded as ‘base64’.

escape If defined, the first character of this option gives the character to use in
place of ‘~’ to denote TILDE ESCAPES.

expandaddr
If not set then file and command pipeline targets are not allowed, and any such
address will be filtered out, giving a warning message. If set without a value
then all possible recipient address specifications will be accepted – see the
section Sending mail for more on this. To accept them, but only in interactive
mode, or when tilde commands were enabled explicitly by using one of the command
line options -~ or -#, set this to the (case-insensitive) value ‘restrict’ (note
right now this is actually like setting ‘restrict,-all,+name,+addr’).

In fact the value is interpreted as a comma-separated list of values. If it
contains ‘fail’ then the existence of disallowed specifications is treated as a
hard send error instead of only filtering them out. The remaining values specify
wether a specific type of recipient address specification is allowed (optionally
indicated by a plus sign ‘+’ prefix) or disallowed (prefixed with a hyphen ‘-’).
The value ‘all’ addresses all possible address specifications, ‘file’ file
targets, ‘pipe’ command pipeline targets, ‘name’ plain user names and (MTA)
aliases ([Obsolete] ‘noalias’ may be used as an alternative syntax to ‘-name’)
and ‘addr’ network addresses. These kind of values are interpreted in the given
order, so that ‘restrict,fail,+file,-all,+addr’ will cause hard errors for any
non-network address recipient address unless S-nail is in interactive mode or has
been started with the -~ or -# command line option; in the latter case(s) any
address may be used, then.

expandargv
Unless this variable is set additional mail-transfer-agent (MTA) arguments from
the command line, as can be given after a ‘--’ separator, are ignored due to
safety reasons. However, if set to the special value ‘fail’, then the presence
of additional MTA arguments is treated as a hard error that causes S-nail to exit
with failure status. A lesser strict variant is the otherwise identical
‘restrict’, which does accept such arguments in interactive mode, or if tilde
commands were enabled explicitly by using one of the command line options -~ or
-#.

features (Read-only) Information on the features compiled into S-nail – the content of
this variable is identical to the output of the command features.

file-hook-load-EXTENSION, file-hook-save-EXTENSION
It is possible to install file hooks which will be used by the file command in
order to be able to transparently handle (through an intermediate temporary file)
files with specific ‘EXTENSION’s: the variable values can include shell snippets
and are expected to write data to standard output / read data from standard
input, respectively. [v15 behaviour may differ] The variables may not be changed
while there is a mailbox attendant.

set file-hook-load-xy='echo >&2 XY-LOAD; gzip -cd' \
file-hook-save-xy='echo >&2 XY-SAVE; gzip -c' \
record=+null-sent.xy

folder The name of the directory to use for storing folders of messages. All folder
names that begin with ‘+’ refer to files below it. The same special conventions
as documented for the file command may be used when specifying a new value for
folder, but be aware that the expansion is fully performed immediately. E.g., if
the expanded name refers to an IMAP account, all names that begin with `+' refer
to IMAP mailboxes below the folder target box.

Note: some IMAP servers do not accept the creation of mailboxes in the hierarchy
base, but require that they are created as subfolders of `INBOX' – with such
servers a folder name of the form

imaps://mylogin@imap.myisp.example/INBOX.

should be used (the last character is the server's hierarchy delimiter). Folder
names prefixed by `+' will then refer to folders below `INBOX', while folder
names prefixed by `@' refer to folders below the hierarchy base. See the imap
namespace command for a method to detect the appropriate prefix and delimiter.

folder-hook
When a folder is opened and this variable is set, the macro corresponding to the
value of this variable is executed. The macro is also invoked when new mail
arrives, but message lists for commands executed from the macro only include
newly arrived messages then. If localopts are activated in a folder hook, then
the covered settings will be reverted once the folder is left again.

folder-hook-FOLDER
Overrides folder-hook for a folder named ‘FOLDER’. Unlike other folder
specifications, the fully expanded name of a folder, without metacharacters, is
used to avoid ambiguities. However, if the mailbox resides under folder then the
usual ‘+’ specification is tried in addition, e.g., if folder is “mail” (and thus
relative to the user's home directory) then /home/usr1/mail/sent will be tried as
‘folder-hook-/home/usr1/mail/sent’ first, but then followed by
‘folder-hook-+sent’.

followup-to-honour
Controls wether a ‘Mail-Followup-To:’ header is honoured when group-replying to a
message via reply or Lreply. This is a quadoption; if set without a value it
defaults to “yes”. Also see followup-to and the commands mlist and mlsubscribe.

from The address (or a list of addresses) to put into the ‘From:’ field of the message
header, quoting RFC 5322: the author(s) of the message, that is, the mailbox(es)
of the person(s) or system(s) responsible for the writing of the message. If
replying to messages these addresses are handled as if they were in the
alternates list. If the machine's hostname is not valid at the Internet (for
example at a dialup machine) then either this variable or hostname ([v15-compat]
and with smtp smtp-hostname adds even more fine-tuning capabilities), have to be
set. If from contains more than one address, setting the sender variable is
required (according to the standard RFC 5322).

fwdheading
The string to print before the text of a message with the forward command (unless
the forward-as-attachment variable is set). Defaults to “-------- Original
Message --------” if unset; No heading is printed if it is set to the empty
string.

headline A format string to use for the header summary, similar to printf(3) formats. A
percent character ‘%’ introduces a format specifier that may be followed by a
number indicating the field width; If the (possibly implicitly implied) field
width is negative, the field is to be left-aligned. Valid format specifiers are:

‘%%’ A plain percent character.
‘%>’ A space character but for the current message, for which it expands
to ‘>’.
‘%<’ A space character but for the current message, for which it expands
to ‘<’.
‘%$’ [Option] The spam score of the message, as has been classified via
the command spamrate. Prints only a replacement character if there
is no spam support.
‘%a’ Message attribute character (status flag); the actual content can be
adjusted by setting attrlist.
‘%d’ The date when the message was received.
‘%e’ The indenting level in threaded mode.
‘%f’ The address of the message sender.
‘%i’ The message thread structure. (Note that this format doesn't support
a field width.)
‘%l’ The number of lines of the message.
‘%m’ Message number.
‘%o’ The number of octets (bytes) in the message.
‘%s’ Message subject (if any).
‘%S’ Message subject (if any) in double quotes.
‘%T’ Message recipient flags: is the addressee of the message a known or
subscribed mailing list – see mlist and mlsubscribe.
‘%t’ The position in threaded/sorted order.

The default is ‘%>%a%m %-18f %16d %4l/%-5o %i%-s’, or
‘%>%a%m %20-f %16d %3l/%-5o %i%-S’ if bsdcompat is set. Also see attrlist and
headline-bidi.

headline-bidi
Bidirectional text requires special treatment when displaying headers, because
numbers (in dates or for file sizes etc.) will not affect the current text
direction, in effect resulting in ugly line layouts when arabic or other right-
to-left text is to be displayed. On the other hand only a minority of terminals
is capable to correctly handle direction changes, so that user interaction is
necessary for acceptable results. Note that extended host system support is
required nonetheless, e.g., detection of the terminal character set is one
precondition; and this feature only works in an Unicode (i.e., UTF-8) locale.

In general setting this variable will cause S-nail to encapsulate text fields
that may occur when printing headline (and some other fields, like dynamic
expansions in prompt) with special Unicode control sequences; it is possible to
fine-tune the terminal support level by assigning a value: no value (or any value
other than ‘1’, ‘2’ and ‘3’) will make S-nail assume that the terminal is capable
to properly deal with Unicode version 6.3, in which case text is embedded in a
pair of U+2068 (FIRST STRONG ISOLATE) and U+2069 (POP DIRECTIONAL ISOLATE)
characters. In addition no space on the line is reserved for these characters.

Weaker support is chosen by using the value ‘1’ (Unicode 6.3, but reserve the
room of two spaces for writing the control sequences onto the line). The values
‘2’ and ‘3’ select Unicode 1.1 support (U+200E, LEFT-TO-RIGHT MARK); the latter
again reserves room for two spaces in addition.

hostname Use this string as hostname when expanding local addresses instead of the value
obtained from uname(3) and getaddrinfo(3), i.e., in ‘Message-ID:’ and ‘From:’
fields. Note that when smtp transport is not used then it is normally the
responsibility of the MTA to create these fields, [v15-compat] in conjunction
with smtp however smtp-hostname also influences the results; you should produce
some test messages with the desired combination of hostname, and/or from, sender
etc. first.

imap-auth-USER@HOST, imap-auth
[Option] Sets the IMAP authentication method. Valid values are `login' for the
usual password-based authentication (the default), `cram-md5', which is a
password-based authentication that does not send the password over the network in
clear text, and `gssapi' for GSS-API based authentication.

imap-cache
[Option] Enables caching of IMAP mailboxes. The value of this variable must
point to a directory that is either existent or can be created by S-nail. All
contents of the cache can be deleted by S-nail at any time; it is not safe to
make assumptions about them.

imap-keepalive-USER@HOST, imap-keepalive-HOST, imap-keepalive
[Option] IMAP servers may close the connection after a period of inactivity; the
standard requires this to be at least 30 minutes, but practical experience may
vary. Setting this variable to a numeric `value' greater than 0 causes a `NOOP'
command to be sent each `value' seconds if no other operation is performed.

imap-list-depth
[Option] When retrieving the list of folders on an IMAP server, the folders
command stops after it has reached a certain depth to avoid possible infinite
loops. The value of this variable sets the maximum depth allowed. The default
is 2. If the folder separator on the current IMAP server is a slash `/', this
variable has no effect and the folders command does not descend to subfolders.

indentprefix
String used by the ~m, ~M and ~R TILDE ESCAPES and by the quote option for
indenting messages, in place of the normal tabulator character ‘^I’, which is the
default. Be sure to quote the value if it contains spaces or tabs.

line-editor-cursor-right
[Option] If the builtin command line editor is used, actions which are based on
rightwise movement may not work on some terminals. If you encounter such
problems, set this variable to the terminal control sequence that is necessary to
move the cursor one column to the right. The default is ‘\033[C’, which should
work for most terminals. Less often occur ‘\033OC’ and ‘\014’. Note that
“Escape” and other control character have to be written as shell-style escape
sequences, e.g., ‘\033’ for (US-ASCII) “Escape”.

MAIL Is used as the user's mailbox, if set. Otherwise, a system-dependent default is
used. Supports a logical subset of the special conventions that are documented
for the file command and the folder option.

mime-counter-evidence
Normally the ‘Content-Type:’ field is used to decide how to handle MIME parts.
Some MUAs however don't use mime.types(5) or a similar mechanism to correctly
classify content, but simply specify ‘application/octet-stream’, even for plain
text attachments like ‘text/diff’. If this variable is set then S-nail will try
to classify such MIME message parts on its own, if possible, and through their
file name. This variable can also be given a non-empty value, in which case the
value is expected to be a number, actually a carrier of bits. Creating the bit-
carrying number is a simple addition:

? !echo Value should be set to $((2 + 4))
Value should be set to 6

· If bit two is set (2) then the detected content-type will be carried along
with the message and be used for deciding which pipe-TYPE/SUBTYPE is
responsible for the MIME part, shall that question arise; when displaying
such a MIME part the part-info will indicate the overridden content-type by
showing a plus-sign ‘+’.
· If bit three is set (4) then the counter-evidence is always produced and a
positive result will be used as the MIME type, even forcefully overriding the
parts given MIME type.

mimetypes-load-control
This option can be used to control which of the mime.types(5) databases are
loaded by S-nail, as furtherly described in the section The mime.types files. If
the letter ‘u’ is part of the option value, then the user's personal
~/.mime.types file will be loaded (if it exists); likewise the letter ‘s’
controls loading of the system wide /etc/mime.types; the user file is loaded
first, letter matching is case-insensitive. If this option is not set S-nail
will try to load both files instead. Incorporation of the S-nail-builtin MIME
types cannot be suppressed, but they will be matched last.

More sources can be specified by using a different syntax: if the value string
contains an equals sign ‘=’ then it is instead parsed as a comma-separated list
of the described letters plus ‘f=FILENAME’ pairs; the given filenames will be
expanded and loaded, and their content may use the extended syntax that is
described in the section The mime.types files.

NAIL_EXTRA_RC
The name of an optional startup file to be read after ~/.mailrc. This variable
has an effect only if it is set in s-nail.rc or ~/.mailrc, it is not imported
from the environment in order to honour ‘MAILRC=/dev/null/’ -n invocations. Use
this file for commands that are not understood by other POSIX mailx(1)
implementations.

NAIL_HEAD A string to put at the beginning of each new message. The escape sequences
tabulator ‘\t’ and newline ‘\n’ are understood.

NAIL_HISTFILE
[Option] If a command line editor is available then this can be set to name the
(expandable) path of the location of a permanent history file.

NAIL_HISTSIZE
[Option] If a command line editor is available this value restricts the amount of
history entries that are saved into a set and valid NAIL_HISTFILE. A value of
less than 0 disables this feature; note that loading and incorporation of
NAIL_HISTFILE upon program startup can also be suppressed by doing this. An
unset or invalid value, or 0, causes a default value to be used. Dependent on
the available command line editor this will also define the number of history
entries in memory; it is also editor-specific wether runtime updates of this
value will be honoured.

NAIL_TAIL A string to put at the end of each new message. The escape sequences tabulator
‘\t’ and newline ‘\n’ are understood.

newfolders
If this variable has the value ‘maildir’, newly created local folders will be in
Maildir format.

newmail Checks for new mail in the current folder each time the prompt is printed. For
IMAP mailboxes the server is then polled for new mail, which may result in
delayed operation if the connection to the server is slow. A Maildir folder must
be re-scanned to determine if new mail has arrived.

If this variable is set to the special value “nopoll” an IMAP server is not
actively asked for new mail, but new mail may still be detected and announced
with any other IMAP command that is sent to the server. In either case the IMAP
server may send notifications about messages that have been deleted on the server
by another process or client. In this case, “Expunged X messages” is printed
regardless of this variable, and message numbers may have changed.

If this variable is set to the special value ‘nopoll’ then a Maildir folder will
not be rescanned completely, but only timestamp changes are detected.

ORGANIZATION
The value to put into the ‘Organization:’ field of the message header.

password-USER@HOST, password-HOST, password
[v15-compat] Variable chain that sets a password, which is used in case none has
been given in the protocol and account-specific URL; as a last resort S-nail will
ask for a password on the user's terminal if the authentication method requires a
password. Specifying passwords in a startup file is generally a security risk;
the file should be readable by the invoking user only.

password-USER@HOST
[no v15-compat] (see the chain above for [v15-compat]) Set the password for
‘USER’ when connecting to ‘HOST’. If no such variable is defined for a host, the
user will be asked for a password on standard input. Specifying passwords in a
startup file is generally a security risk; the file should be readable by the
invoking user only.

pipe-TYPE/SUBTYPE
When a MIME message part of type ‘TYPE/SUBTYPE’ (normalized to lowercase) is
displayed or quoted, its text is filtered through the value of this variable
interpreted as a shell command. The special value ‘@’ can be used to force
interpretation of the message part as plain text, e.g., ‘set
pipe-application/pgp-signature=@’ will henceforth treat signatures as plain text
and display them "as is". (The same can also be achieved, in a more useful
context, by using the mimetype command in conjunction with a type marker.)

Also, if a shell command is prefixed with ‘@’, then the command will only be used
to prepare the MIME message part if the message is displayed by itself, but not
when multiple messages are displayed at once.

Finally, if a shell command is prefixed with ‘@&’, then, in addition to what has
been described for the plain ‘@’ shell command prefix, the command will be run
asynchronously, i.e., without blocking S-nail, which may be a handy way to
display a, e.g., PDF file while also continuing to read the mail message. Some
information about the MIME part to be displayed is embedded into the environment
of the shell command:

NAIL_TMPDIR The temporary directory that S-nail uses. Usually
identical to TMPDIR, but guaranteed to be set and usable
by child processes; to ensure the latter condition for
TMPDIR also, it'll be set.
NAIL_FILENAME The filename, if any is set, the empty string otherwise.
NAIL_FILENAME_GENERATED A random string.
NAIL_CONTENT The MIME content-type of the part, if known, the empty
string otherwise.
NAIL_CONTENT_EVIDENCE If mime-counter-evidence includes the carry-around-bit
(2), then this will be set to the detected MIME content-
type; not only then identical to NAIL_CONTENT otherwise.

pipe-EXTENSION
This is identical to pipe-TYPE/SUBTYPE except that ‘EXTENSION’ (normalized to
lowercase using character mappings of the ASCII charset) names a file extension,
e.g., ‘xhtml’. Handlers registered using this method take precedence.

pop3-keepalive-USER@HOST, pop3-keepalive-HOST, pop3-keepalive
[Option] POP3 servers close the connection after a period of inactivity; the
standard requires this to be at least 10 minutes, but practical experience may
vary. Setting this variable to a numeric value greater than ‘0’ causes a ‘NOOP’
command to be sent each value seconds if no other operation is performed.

prompt The string printed when a command is accepted. Prompting may be prevented by
either setting this to the null string or by setting noprompt. The same XSI
escape sequences that are understood by the echo command may be used within
prompt.

In addition, the following S-nail specific additional sequences are understood:
‘\&’, which expands to “?” unless bsdcompat is set, in which case it expands to
“&”; note that ‘\& ’ is the default value of prompt. ‘\?’, which will expand to
“1” if the last command failed and to “0” otherwise, ‘\$’, which will expand to
the name of the currently active account, if any, and to the empty string
otherwise, and ‘\@’, which will expand to the name of the currently active
mailbox. (Note that the prompt buffer is size-limited, excess is cut off.)

Even though prompt checks for headline-bidi to encapsulate the expansions of the
‘\$’ and ‘\@’ escape sequences as necessary to correctly display bidirectional
text, this is not true for the final string that makes up prompt as such, i.e.,
real BIDI handling is not supported.

When a newer version of the editline(3) Command line editor is used, any escape
sequence must itself be encapsulated with another escape character for usage with
the EL_PROMPT_ESC mechanism: S-nail configures the control character ‘\01’ for
this.

quote If set, S-nail starts a replying message with the original message prefixed by
the value of the variable indentprefix. Normally, a heading consisting of
“Fromheaderfield wrote:” is printed before the quotation. If the string
‘noheading’ is assigned to the quote variable, this heading is omitted. If the
string ‘headers’ is assigned, the headers selected by the ignore/retain commands
are printed above the message body, thus quote acts like an automatic `~m' TILDE
ESCAPES command, then. If the string ‘allheaders’ is assigned, all headers are
printed above the message body and all MIME parts are included, making quote act
like an automatic `~M' command; also see quote-as-attachment.

quote-fold
[Option] Can be set in addition to indentprefix. Setting this turns on a more
fancy quotation algorithm in that leading quotation characters are compressed and
overlong lines are folded. quote-fold can be set to either one or two (space
separated) numeric values, which are interpreted as the maximum (goal) and the
minimum line length, respectively, in a spirit rather equal to the fmt(1)
program, but line-, not paragraph-based. If not set explicitly the minimum will
reflect the goal algorithmically. The goal can't be smaller than the length of
indentprefix plus some additional pad. Necessary adjustments take place
silently.

record If defined, gives the pathname of the folder used to record all outgoing mail.
If not defined, then outgoing mail is not saved. When saving to this folder
fails the message is not sent, but instead saved to DEAD.

reply_strings
Can be set to a comma-separated list of (case-insensitive according to ASCII
rules) strings which shall be recognized in addition to the builtin strings as
‘Subject:’ reply message indicators – builtin are ‘Re:’, which is mandated by RFC
5322, as well as the german ‘Aw:’.

replyto A list of addresses to put into the ‘Reply-To:’ field of the message header.
Members of this list are handled as if they were in the alternates list.

reply-to-honour
Controls wether a ‘Reply-To:’ header is honoured when replying to a message via
reply or Lreply. This is a quadoption; if set without a value it defaults to
“yes”.

screen When S-nail initially prints the message headers it determines the number to
print by looking at the speed of the terminal. The faster the terminal, the more
it prints. This option overrides this calculation and specifies how many message
headers are printed. This number is also used for scrolling with the z command.

sendcharsets
[Option] A comma-separated list of character set names that can be used in
outgoing internet mail. The value of the variable charset-8bit is automatically
appended to this list of character-sets. If no character set conversion
capabilities are compiled into S-nail then the only supported charset is
ttycharset. Also see sendcharsets-else-ttycharset and refer to the section
Character sets for the complete picture of character set conversion in S-nail.

sender An address that is put into the ‘Sender:’ field of outgoing messages, quoting RFC
5322: the mailbox of the agent responsible for the actual transmission of the
message. This field should normally not be used unless the ‘From:’ field
contains more than one address, on which case it is required. The sender address
is handled as if it were in the alternates list.

sendmail To use an alternate mail transport agent (MTA), set this option to the full
pathname of the program to use. It may be necessary to set sendmail-progname in
addition.

The MTA will be passed command line arguments from several possible sources: from
the variable sendmail-arguments if set, from the command line if given and the
variable expandargv allows their use. Argument processing of the MTA will always
be terminated with a ‘--’ separator.

The otherwise occurring implicit usage of the following MTA command line
arguments can be disabled by setting the binary option
sendmail-no-default-arguments: ‘-i’ (for not treating a line with only a dot ‘.’
character as the end of input), ‘-m’ (shall the option metoo be set) and ‘-v’ (if
the verbose option is set); in conjunction with the -r command line option S-nail
will also pass ‘-f’ as well as ‘-F’.

sendmail-arguments
Arguments to pass through to the Mail-Transfer-Agent can be given via this
option. The content of this variable will be split up in a vector of arguments
which will be joined onto other possible MTA options:

set sendmail-arguments='-t -X "/tmp/my log"'

sendmail-no-default-arguments
(Binary) Unless this option is set S-nail will pass some well known standard
command line options to the defined sendmail program, see there for more.

sendmail-progname
Many systems use a so-called mailwrapper(8) environment to ensure compatibility
with sendmail(1). This works by inspecting the name that was used to invoke the
mail delivery system. If this variable is set then the mailwrapper (the program
that is actually executed when calling “sendmail”) will treat its contents as
that name. The default is ‘sendmail’.

Sign A string for use with the ~A tilde escape.

sign A string for use with the ~a tilde escape.

signature Must correspond to the name of a readable file if set. The file's content is
then appended to each singlepart message and to the first part of each multipart
message. Be warned that there is no possibility to edit the signature for an
individual message.

smime-ca-dir
[Option] Specifies a directory with CA certificates in PEM (Privacy Enhanced
Mail) format for verification of S/MIME signed messages.

smime-ca-file
[Option] Specifies a file with CA certificates in PEM format for verification of
S/MIME signed messages.

smime-cipher-USER@HOST, smime-cipher
[Option] Specifies the cipher to use when generating S/MIME encrypted messages
(for the specified account). RFC 5751 mandates a default of ‘aes128’ (AES-128
CBC). Possible values are (case-insensitive and) in decreasing cipher strength:
‘aes256’ (AES-256 CBC), ‘aes192’ (AES-192 CBC), ‘aes128’ (AES-128 CBC), ‘des3’
(DES EDE3 CBC, 168 bits; default if ‘aes128’ isn't available) and ‘des’ (DES CBC,
56 bits).

The actually available cipher algorithms depend on the cryptographic library that
S-nail uses. [Option] Support for more cipher algorithms may be available
through dynamic loading via, e.g., EVP_get_cipherbyname(3) (OpenSSL) if S-nail
has been compiled to support this.

smime-crl-dir
[Option] Specifies a directory that contains files with CRLs in PEM format to use
when verifying S/MIME messages.

smime-crl-file
[Option] Specifies a file that contains a CRL in PEM format to use when verifying
S/MIME messages.

smime-encrypt-USER@HOST
[Option] If this variable is set, messages send to the given receiver are
encrypted before sending. The value of the variable must be set to the name of a
file that contains a certificate in PEM format.

If a message is sent to multiple recipients, each of them for whom a
corresponding variable is set will receive an individually encrypted message;
other recipients will continue to receive the message in plain text unless the
smime-force-encryption variable is set. It is recommended to sign encrypted
messages, i.e., to also set the smime-sign variable.

smime-sign-cert-USER@HOST, smime-sign-cert
[Option] Points to a file in PEM format. For the purpose of signing and
decryption this file needs to contain the user's private key as well as his
certificate.

For message signing ‘USER@HOST’ is always derived from the value of from (or, if
that contains multiple addresses, sender). For the purpose of encryption the
recipient's public encryption key (certificate) is expected; the command certsave
can be used to save certificates of signed messages (the section Signed and
encrypted messages with S/MIME gives some details). This mode of operation is
usually driven by the specialized form.

When decrypting messages the account is derived from the recipient fields (‘To:’
and ‘Cc:’) of the message, which are searched for addresses for which such a
variable is set. S-nail always uses the first address that matches, so if the
same message is sent to more than one of the user's addresses using different
encryption keys, decryption might fail.

smime-sign-include-certs-USER@HOST, smime-sign-include-certs
[Option] If used, this is supposed to a consist of a comma-separated list of
files, each of which containing a single certificate in PEM format to be included
in the S/MIME message in addition to the smime-sign-cert certificate. This is
most useful for long certificate chains if it is desired to aid the receiving
party's verification process. Note that top level certificates may also be
included in the chain but don't play a role for verification. Also see
smime-sign-cert. Remember that for this ‘USER@HOST’ refers to the variable from
(or, if that contains multiple addresses, sender).

smime-sign-message-digest-USER@HOST, smime-sign-message-digest
[Option] Specifies the message digest to use when signing S/MIME messages. RFC
5751 mandates a default of ‘sha1’. Possible values are (case-insensitive and) in
decreasing cipher strength: ‘sha512’, ‘sha384’, ‘sha256’, ‘sha224’ and ‘md5’.

The actually available message digest algorithms depend on the cryptographic
library that S-nail uses. [Option] Support for more message digest algorithms
may be available through dynamic loading via, e.g., EVP_get_digestbyname(3)
(OpenSSL) if S-nail has been compiled to support this. Remember that for this
‘USER@HOST’ refers to the variable from (or, if that contains multiple addresses,
sender).

smtp [Option] Normally S-nail invokes the program defined via sendmail to transfer
messages, as described in Sending mail. Setting the smtp variable will instead
cause SMTP network connections be made to the server specified therein in order
to directly submit the message. S-nail knows about three different “SMTP
protocols”:

· The plain SMTP protocol (RFC 5321) that normally lives on the server port 25
and requires setting the smtp-use-starttls variable to enter a SSL/TLS
encrypted session state. Assign a value like [v15-compat]
‘[smtp://][user[:password]@]server[:port]’ ([no v15-compat]
‘[smtp://]server[:port]’) to choose this protocol.
· Then the so-called SMTPS which is supposed to live on server port 465 and is
automatically SSL/TLS secured. Unfortunately it never became a standardized
protocol and may thus not be supported by your hosts network service database
– in fact the port number has already been reassigned to other protocols!

SMTPS is nonetheless a commonly offered protocol and thus can be chosen by
assigning a value like [v15-compat] ‘smtps://[user[:password]@]server[:port]’
([no v15-compat] ‘smtps://server[:port]’); due to the mentioned problems it
is usually necessary to explicitly specify the port as ‘:465’, however.
· Finally there is the SUBMISSION protocol (RFC 6409), which usually lives on
server port 587 and is practically identically to the SMTP protocol from
S-nails point of view beside that; it requires setting the smtp-use-starttls
variable to enter a SSL/TLS secured session state. Assign a value like
[v15-compat] ‘submission://[user[:password]@]server[:port]’ ([no v15-compat]
‘submission://server[:port]’).

For more on credentials etc. please see On URL syntax and credential lookup. The
SMTP transfer is executed in a child process, which runs asynchronously unless
either the sendwait or the verbose variable is set. If it receives a TERM
signal, it will abort and save the message to DEAD.

smtp-auth-USER@HOST, smtp-auth-HOST, smtp-auth
[Option] Variable chain that sets the SMTP authentication method. Possible
values are ‘none’ ([no v15-compat] default), ‘plain’ ([v15-compat] default),
‘login’ as well as the [Option]al methods ‘cram-md5’ and ‘gssapi’. The ‘none’
method doesn't need any user credentials, ‘gssapi’ requires a user name and all
other methods require a user name and a password. See [v15-compat] smtp, user
and password ([no v15-compat] smtp-auth-password and smtp-auth-user). Note that
smtp-auth-HOST is [v15-compat]. [no v15-compat]: Note for smtp-auth-USER@HOST:
may override dependend on sender address in the variable from.

smtp-auth-password
[Option] [no v15-compat] Sets the global fallback password for SMTP
authentication. If the authentication method requires a password, but neither
smtp-auth-password nor a matching smtp-auth-password-USER@HOST can be found,
S-nail will ask for a password on the user's terminal.

smtp-auth-password-USER@HOST
[no v15-compat] Overrides smtp-auth-password for specific values of sender
addresses, dependent upon the variable from.

smtp-auth-user
[Option] [no v15-compat] Sets the global fallback user name for SMTP
authentication. If the authentication method requires a user name, but neither
smtp-auth-user nor a matching smtp-auth-user-USER@HOST can be found, S-nail will
ask for a user name on the user's terminal.

smtp-auth-user-USER@HOST
[no v15-compat] Overrides smtp-auth-user for specific values of sender addresses,
dependent upon the variable from.

smtp-hostname
[v15-compat] Normally S-nail uses the variable from to derive the necessary
‘USER@HOST’ information to issue a ‘MAIL FROM:<>’ SMTP command. Setting
smtp-hostname can be used to use the ‘USER’ from the SMTP account (smtp or the
user variable chain) and the ‘HOST’ from the content of this variable (or, if
that is the empty string, hostname or the local hostname as a last resort). This
often allows using an address that is itself valid but hosted by a provider other
than which (in from) is about to send the message. Setting this variable also
influences the generated ‘Message-ID:’.

spam-interface
[Option] In order to use any of the spam-related commands (like, e.g., spamrate)
the desired spam interface must be defined by setting this variable. Please
refer to the manual section Handling spam for the complete picture of spam
handling in S-nail. All or none of the following interfaces may be available:

‘spamc’ Interaction with spamc(1) from the spamassassin(1)
(http://spamassassin.apache.org SpamAssassin) suite. Different to the
generic filter interface S-nail will automatically add the correct
arguments for a given command and has the necessary knowledge to parse
the program's output. A default value for spamc-command will have been
compiled into the S-nail binary if spamc(1) has been found in PATH
during compilation. Shall it be necessary to define a specific
connection type (rather than using a configuration file for that), the
variable spamc-arguments can be used as in, e.g., ‘-d
server.example.com -p 783’. It is also possible to specify a per-user
configuration via spamc-user. Note that this interface doesn't inspect
the ‘is-spam’ flag of a message for the command spamforget.

‘spamd’ S-nail will directly communicate with the spamassassin(1) daemon
spamd(1) via a path-based unix(4) stream socket as specified in
spamd-socket. It is possible to specify a per-user configuration via
spamd-user.

‘filter’ generic spam filter support via freely configurable hooks. This
interface is ment for programs like bogofilter(1) and sylfilter(1) and
requires according behaviour in respect to the hooks' exit status for
at least the command spamrate (‘0’ meaning a message is spam, ‘1’ for
non-spam, ‘2’ for unsure and any other return value indicating a hard
error); since the hooks can include shell code snippets diverting
behaviour can be intercepted as necessary. The hooks are
spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate
and spamfilter-spam; the manual section Handling spam contains examples
for some programs. The process environment of the hooks will have the
variables NAIL_TMPDIR, TMPDIR and NAIL_FILENAME_GENERATED set. Note
that spam score support for spamrate isn't supported unless the
[Option]tional regular expression support is available and the
spamfilter-rate-scanscore variable is set.

spam-maxsize
[Option] Messages that exceed this size won't be passed through to the configured
spam-interface. The default is 420000 bytes.

spamc-command
[Option] The path to the spamc(1) program for the ‘spamc’ spam-interface. Note
that the path is not expanded, but used “as is”. A fallback path will have been
compiled into the S-nail binary if the executable had been found during
compilation.

spamc-arguments
[Option] Even though S-nail deals with most arguments for the ‘spamc’
spam-interface automatically, it may at least sometimes be desirable to specifiy
connection-related ones via this variable, e.g., ‘-d server.example.com -p 783’.

spamc-user
[Option] Specify a username for per-user configuration files for the ‘spamc’
spam-interface. If this is set to the empty string then S-nail will use the name
of the current user.

spamd-socket
[Option] Specify the path of the unix(4) domain socket on which spamd(1) listens
for connections for the ‘spamd’ spam-interface. Note that the path is not
expanded, but used “as is”.

spamd-user
[Option] Specify a username for per-user configuration files for the ‘spamd’
spam-interface. If this is set to the empty string then S-nail will use the name
of the current user.

spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate, spamfilter-spam
[Option] Command and argument hooks for the ‘filter’ spam-interface. The manual
section Handling spam contains examples for some programs.

spamfilter-rate-scanscore
[Option] Because of the generic nature of the ‘filter’ spam-interface spam scores
are not supported for it by default, but if the [Option]tional regular expression
support is available then setting this variable can be used to overcome this
restriction. It is interpreted as follows: first a number (digits) is parsed
that must be followed by a semicolon ‘;’ and a regular expression. Then the
latter is used to parse the first output line of the spamfilter-rate hook, and,
in case the evaluation is successful, the group that has been specified via the
number is interpreted as a floating point scan score.

ssl-ca-dir
[Option] Specifies a directory with CA certificates in PEM (Pricacy Enhanced
Mail) for verification of of SSL/TLS server certificates. See
SSL_CTX_load_verify_locations(3) for more information.

ssl-ca-file
[Option] Specifies a file with CA certificates in PEM format for verification of
SSL/TLS server certificates. See SSL_CTX_load_verify_locations(3) for more
information.

ssl-cert-USER@HOST, ssl-cert-HOST, ssl-cert
[Option] Variable chain that sets the file name for a SSL/TLS client certificate
required by some servers. This is a direct interface to the ‘Certificate’ slot
of the SSL_CONF_cmd(3) function of the OpenSSL library, if available.

ssl-cipher-list-USER@HOST, ssl-cipher-list-HOST, ssl-cipher-list
[Option] Specifies a list of ciphers for SSL/TLS connections. This is a direct
interface to the ‘CipherString’ slot of the SSL_CONF_cmd(3) function of the
OpenSSL library, if available; see ciphers(1) for more information. By default
S-nail doesn't set a list of ciphers, which in effect will use a ssl-protocol
specific cipher (protocol standards ship with a list of acceptable ciphers),
possibly cramped to what the actually used SSL/TLS library supports – the manual
section An example configuration also contains a SSL/TLS use case.

ssl-config-file
[Option] If this variable is set S-nail will call CONF_modules_load_file(3) to
allow OpenSSL to be configured according to the host system wide security
settings. If a non-empty value is given then this will be used to specify the
configuration file to be used instead of the global OpenSSL default; note that in
this case it is an error if the file cannot be loaded. The application name will
always be passed as “s-nail”.

ssl-crl-file
[Option] Specifies a file that contains a CRL in PEM format to use when verifying
SSL/TLS server certificates.

ssl-crl-dir
[Option] Specifies a directory that contains files with CRLs in PEM format to use
when verifying SSL/TLS server certificates.

ssl-key-USER@HOST, ssl-key-HOST, ssl-key
[Option] Variable chain that sets the file name for the private key of a SSL/TLS
client certificate. If unset, the name of the certificate file is used. The
file is expected to be in PEM format. This is a direct interface to the
‘PrivateKey’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if
available.

ssl-method-USER@HOST, ssl-method-HOST, ssl-method
[Option] [Obsolete] Please use the newer and more flexible ssl-protocol instead:
if both values are set, ssl-protocol will take precedence! Can be set to the
following values, the actually used ssl-protocol specification to which it is
mapped is shown in parenthesis: ‘tls1.2’ (‘-ALL, TLSv1.2’), ‘tls1.1’ (‘-ALL,
TLSv1.1’), ‘tls1’ (‘-ALL, TLSv1’) and ‘ssl3’ (‘-ALL, SSLv3’); the special value
‘auto’ is mapped to ‘ALL, -SSLv2’ and thus includes the SSLv3 protocol. Note
that SSLv2 is no longer supported at all.

ssl-protocol-USER@HOST, ssl-protocol-HOST, ssl-protocol
[Option] Specify the used SSL/TLS protocol. This is a direct interface to the
‘Protocol’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if
available; otherwise an S-nail internal parser is used which understands the
following subset of (case-insensitive) command strings: ‘SSLv3’, ‘TLSv1’,
‘TLSv1.1’ and ‘TLSv1.2’, as well as the special value ‘ALL’. Multiple
specifications may be given via a comma-separated list which ignores any
whitespace. An optional ‘+’ plus prefix will enable a protocol, a ‘-’ minus
prefix will disable it, so that ‘-ALL, TLSv1.2’ will enable only the TLSv1.2
protocol.

It depends upon the used TLS/SSL library which protocols are actually supported
and which protocols are used if ssl-protocol is not set, but note that SSLv2 is
no longer supported at all and actively disabled. Especially for older protocols
explicitly securing ssl-cipher-list may be worthwile, see An example
configuration.

ssl-rand-egd
[Option] Gives the pathname to an entropy daemon socket, see RAND_egd(3). Not
all SSL/TLS libraries support this.

ssl-rand-file
[Option] Gives the pathname to a file with entropy data, see RAND_load_file(3).
If the file is a regular file writable by the invoking user, new data is written
to it after it has been loaded.

ssl-verify-USER@HOST, ssl-verify-HOST, ssl-verify
[Option] Variable chain that sets the action to be performed if an error occurs
during SSL/TLS server certificate validation. Valid (case-insensitive) values
are ‘strict’ (fail and close connection immediately), ‘ask’ (ask whether to
continue on standard input), ‘warn’ (print a warning and continue), ‘ignore’ (do
not perform validation). The default is ‘ask’.

stealthmua
If only set without an assigned value, then this option inhibits the generation
of the ‘Message-ID:’ and ‘User-Agent:’ header fields that include obvious
references to S-nail. There are two pitfalls associated with this: First, the
message id of outgoing messages is not known anymore. Second, an expert may
still use the remaining information in the header to track down the originating
mail user agent. If set to the value ‘noagent’, then the mentioned ‘Message-ID:’
suppression doesn't occur.

toplines If defined, gives the number of lines of a message to be printed out with the top
command; normally, the first five lines are printed.

ttycharset
The character set of the terminal S-nail operates on, and the one and only
supported character set that S-nail can use if no character set conversion
capabilities have been compiled into it, in which case it defaults to ISO-8859-1
unless it can deduce a value from the LC_CTYPE locale environment. Refer to the
section Character sets for the complete picture about character sets.

user-HOST, user
[v15-compat] Variable chain that sets a global fallback user name, which is used
in case none has been given in the protocol and account-specific URL. This
variable defaults to the value of USER.

version, version-major, version-minor, version-update
(Read-only) S-nail version information: the first variable contains a string
containing the complete version identification – this is identical to the output
of the command version. The latter three contain only digits: the major, minor
and update version numbers.

ENVIRONMENT


The term “environment variable” should be considered an indication that the following
variables are either standardized as being vivid parts of process environments, or are
commonly found in there. Unless otherwise explicitly noted they integrate into the normal
variable handling, as documented above, from S-nails point of view.

COLUMNS
The user's preferred width in column positions for the terminal screen or window.
Queried and used once on program startup.

DEAD The name of the file to use for saving aborted messages if save is set; this
defaults to dead.letter in the user's HOME directory.

EDITOR Pathname of the text editor to use in the edit command and ~e TILDE ESCAPES. A
default editor is used if this value is not defined.

HOME The user's home directory. This variable is only used when it resides in the
process environment. Use setenv to update the value at runtime.

LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES
See locale(7) and Character sets.

LINES The user's preferred number of lines on a page or the vertical screen or window size
in lines. Queried and used once on program startup.

LISTER Pathname of the directory lister to use in the folders command when operating on
local mailboxes. Default is ls(1) (path search through SHELL).

MBOX The name of the user's mbox file. Supports a logical subset of the special
conventions that are documented for the file command and the folder option. The
fallback default is mbox in the user's HOME directory.

MAILRC Is used as a startup file instead of ~/.mailrc if set. When S-nail scripts are
invoked on behalf of other users, this variable should be set to /dev/null to avoid
side-effects from reading their configuration files. This variable is only used
when it resides in the process environment.

NAIL_NO_SYSTEM_RC
If this variable is set then reading of s-nail.rc at startup is inhibited, i.e., the
same effect is achieved as if S-nail had been started up with the option -n. This
variable is only used when it resides in the process environment.

NETRC [v15-compat] [Option] This variable overrides the default location of the user's
.netrc file.

PAGER Pathname of the program to use in the more command or when the crt variable is set.
The default paginator is more(1) (path search through SHELL).

PATH A list of directories that is searched by the shell when looking for commands (as
such only recognized in the process environment).

SHELL The shell to use for the commands !, shell, the ~! TILDE ESCAPES and when starting
subprocesses. A default shell is used if this option is not defined.

SYSV3 Changes the letters printed in the first column of a header summary.

TERM [Option] The terminal type for which output is to be prepared.

TMPDIR Used as directory for temporary files instead of /tmp, if set. This variable is
only used when it resides in the process environment. Use setenv to update the
value at runtime.

USER Force identification as the given user, i.e., identical to the -u command line
option. This variable is only used when it resides in the process environment. Use
setenv to update the value at runtime, but note that doing so won't trigger any of
those validation checks that were performed on program startup (again).

VISUAL Pathname of the text editor to use in the visual command and ~v TILDE ESCAPES.

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