NAME

       expn - recursively expand mail aliases

SYNOPSIS

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

DESCRIPTION

       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.

OPTIONS

       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.

ENVIRONMENT

       No environment variables are used.

FILES

       /tmp/expn$$ temporary file used as input to nslookup.

SEE ALSO

       aliases(5), sendmail(8), nslookup(8), RFC 823, and RFC 1123.

BUGS

       Not  all mail daemons will implement expn or vrfy.  It is not possible to verify addresses
       that are served by such daemons.
       When attempting to connect to a system to verify  an  address,  expn  only  tries  one  IP
       address.  Most mail daemons will try harder.
       It  is  assumed  that  you  are  running  domain names and that the nslookup(8) program is
       available.  If not, expn will not be able to verify many addresses.  It  will  also  pause
       for  a  long  time  unless  you  change  the code where it says $have_nslookup = 1 to read
       $have_nslookup = 0.
       Lastly, expn does not handle every valid address.  If you have an example, please submit a
       bug report.

CREDITS

       In  1986 or so, Jon Broome wrote a program of the same name that did about the same thing.
       It has since suffered bit rot and Jon Broome has dropped off the face of the earth!  (Jon,
       if you are out there, drop me a line)

AVAILABILITY

       The    latest    version    of    expn    is    available   through   anonymous   ftp   at
       ftp://ftp.idiom.com/pub/muir-programs/expn.

AUTHOR

       David Muir Sharnoff    <muir@idiom.com>