EXPN(1)                                                   EXPN(1)



NAME
       expn - recursively expand mail aliases

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

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 for-
       mula.  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 ver-
       bose.  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 enviroment 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  dae-
       mons 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>



                          March 11, 1993                  EXPN(1)