[Mailman-Users] Sender not receiving messages

David Lee t.d.lee at durham.ac.uk
Fri Aug 25 10:55:01 CEST 2006

On Thu, 24 Aug 2006, Allan Trick wrote:

> Getting more reports now of other internal users (we have people
> subscribed within our firewall on our Exchange mail server as well as
> people outside with all other kinds of email addresses) not getting
> all messages.  In each case, it sounds like they get ONE message,
> whereas they're on between 4 and 20 different lists.  They should be
> getting 4-20 copies of the same message (one for each list they're
> on).  But they're only getting ONE.  I can't see anything different
> in the settings for the one successful list (not the same one for all users).
> Is it possible that Exchange is trying to be helpful by not
> delivering the additional messages since they're all the same?  There
> is nothing in the Junk folder, but it seems logical that the mail
> system might be interfering with the mail delivery here.  We just
> went to Exchange; previously we were on sendmail and everything worked OK.

We, too, are doing the initial phases of migrating from Unix based UW-IMAP
towards Exchange.  I think I have seen something similar:  UW-IMAP
recipient on 'n' lists gets 'n' copies; similar Exchange recipient sees
one copy.  (Note the "I think" disclaimer: we haven't yet put this far
enough up the priority list to investigate more fully.)

So before looking at the Mailman configuration, perhaps first check the
email logs (sendmail, exim, etc.) on the Mailman machine to what it is
outputting towards the Exchange server: 'n' or one.  If 'n', then it seems
that Exchange would be conflating them; if one, then you probably need to
concentrate your efforts on the Mailman machine.

(My guess, and it is only a guess, is that Exchange assumes the
"Message-ID" is unique and so discards duplicates.  This uniqueness
assumption for email is generally fine.  But in the case of an email going
through more than one list, with recipients in common, I think it would no
longer be valid.)

Hope that helps.  (You might want to report back your findings for the
benefit of the FAQ!)


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