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expn - Online in the Cloud

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This is the command expn that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator



expn - recursively expand mail aliases


expn [-a] [-v] [-w] [-d] [-1] user[@hostname] [user[@hostname]]...


expn will use the SMTP expn and vrfy commands to expand mail aliases. It will first look
up the addresses you provide on the command line. If those expand into addresses on other
systems, it will connect to the other systems and expand again. It will keep doing this
until no further expansion is possible.


The default output of expn can contain many lines which are not valid email addresses.
With the -aa flag, only expansions that result in legal addresses are used. Since many
mailing lists have an illegal address or two, the single -a, address, flag specifies that
a few illegal addresses can be mixed into the results. More -a flags vary the ratio.
Read the source to track down the formula. With the -a option, you should be able to
construct a new mailing list out of an existing one.

If you wish to limit the number of levels deep that expn will recurse as it traces
addresses, use the -1 option. For each -1 another level will be traversed. So, -111 will
traverse no more than three levels deep.

The normal mode of operation for expn is to do all of its work silently. The following
options make it more verbose. It is not necessary to make it verbose to see what it is
doing because as it works, it changes its argv[0] variable to reflect its current
activity. To see how it is expanding things, the -v, verbose, flag will cause expn to
show each address before and after translation as it works. The -w, watch, flag will
cause expn to show you its conversations with the mail daemons. Finally, the -d, debug,
flag will expose many of the inner workings so that it is possible to eliminate bugs.


No environment variables are used.

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