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RedHat 9 (Linux i386) - man page for expn (redhat section 1)

EXPN(1) 			     General Commands Manual				  EXPN(1)

       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 con-
       struct 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 activ-
       ity.  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 avail-
       able.  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    <muir@idiom.com>

7th Edition				  March 11, 1993				  EXPN(1)

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