modifying mail list by list

Walter Dnes wrote,

| [H]ow do I modify the header of
| incoming mail from this list to include...
| "Reply-To: procmail(_at_)Informatik(_dot_)RWTH-Aachen(_dot_)DE", regardless
| of whether or not it already has a Reply-To: line? 

First, I think that's a bad idea; you should trust the poster's selected
return address.  But I'll answer nonetheless.

| I'd have to check the header for the presence of this list's
| "To:" line and the absence of the appropriate "Reply-To:"
| (In order to avoid infinite looping).
| 
| 0h:
| * ^(To|Cc|Bcc):(_dot_)*procmail(_at_)Informatik(_dot_)RWTH-Aachen(_dot_)DE
| * !^Reply-To:(_dot_)*procmail(_at_)Informatik(_dot_)RWTH-Aachen(_dot_)DE
| {
| 
| Now what do I do ???
| 
| }

Question #1: if someone groupreplies to a post of yours, does the directly
mailed copy count as "incoming mail from this list"?  That's a matter of
personal judgment.

If so,

      :0
      * ^TO_procmail
      * ! 
^(Resent-)?Reply-To:(.*\<)?procmail(_at_)informatik\(_dot_)rwth-aachen\(_dot_)de
      {
       :0fwh
       * ^Resent-
       | formail -i "Reply-To: 
procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de" \
                 -i "Resent-Reply-To: 
procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de"
       :0Efwh
       | formail -i "Reply-To: 
procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de"
      }

If not,

     :0fhw
     * ^Resent-Sender: procmail-request
     * ! 
^(Resent-)?Reply-To:(.*\<)?procmail(_at_)informatik\(_dot_)rwth-aachen\(_dot_)de
     | formail -i "Reply-To: 
procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de" \
               -i "Resent-Reply-To: 
procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de"

I recommend formail's -i option so that the original Reply-To: header,
if there was one, will still be there as Old-Reply-To: to save the original
return address in case you decide to send a private reply.

|   Is it possible with a POPmail client to get sendmail (or
| whatever) to filter *OUTGOING* mail; check for the
| destination; and modify the "Reply-To:" differently
| for each list.  A wishlist item while I'm at it; can
| I similarly append a different signature for one
| specific list, where a person's city of residence is
| pertinent info to the discussion.

Procmail's -m option is ideal for outgoing mail; the question is whether your
MUA can be told to make mail detour through a user-selected filter rather
than making a beeline for the MTA.  If you can, then yes, the procmail rcfile
(suggestion: write a separate rcfile for outgoing mail and don't use your
incoming mail's .procmailrc) can add the particular Reply-To: line or
signature that you want, based on any condition procmail can handle.