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       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

       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.


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


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


       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.


       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)


       The  latest  version  of  expn  is  available  through anonymous ftp at


       David Muir Sharnoff    <>