>  .Mail sent to user1 from another user on the same host are promptly received
>  .whether using the address  user1  or  user1@dom.org   or  user1@hname.dom.org
>  .
> What i would like to figure out is how did the host name 'hname' enter the address. 
> I have always used 'user1@dom.org' in configuration files (alias, ect.); 

Dang.  I had a nice, long reply all typed up, hit send, and then my
machine went haywire due to crond wigging out.  Ran out of processes... :(
I'll try again, though...

I don't think that this is a problem with Mailman.  The best way
to test this is by sending mail to the fully-qualified address
and seeing if it changes in the To: header.  If it stays the way
that you typed it, then you're just dealing with a simple case of
RFC 822 compliance.

All email addresses are supposed to be fully-qualified, although not
all mailers require it.  Newer versions of sendmail (or more accurately,
sendmail.cf files generated under newer versions of sendmail) will
append what it thinks is your domain name onto the end of an 
unqualified address.  I'm assuming that the other major MTAs (like
postfix/exim/qmail/MTA de jour) do this too, since it *is*
The Right Thing(tm).

If you're using sendmail, your domain name is extracted from the
j macro.  You can view its settings by running

   /usr/lib/sendmail -d0.1 -bt < /dev/null

Your output will look something like this:

   Version 8.9.3
    Compiled with: MAP_REGEX LOG MATCHGECOS MIME7TO8 MIME8TO7 NAMED_BIND
                   NETINET NETUNIX NEWDB QUEUE SCANF SMTP USERDB XDEBUG

   ============ SYSTEM IDENTITY (after readcf) ============
         (short domain name) $w = lorien
     (canonical domain name) $j = lorien.mallorn.com
            (subdomain name) $m = mallorn.com
                 (node name) $k = lorien.mallorn.com
   ========================================================

   ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
   Enter <ruleset> <address>

And sure enough, $j shows the value of j.  

You can override sendmail's concept of j by modifying the line
starting with Dj in your sendmail.cf:

   Dj$m

If that doesn't work, try

   Djdom.org

Make sure that you have all of your MX records, etc. in place 
for the canonical domain name as well as the individual
machine that it was referencing before.

If you're using a different MTA, tough noogies.  I haven't played
with them enough to know how to deal with this.  :)

Chris