[Mailman-Users] Eliminating Duplicate Postings

Mark Sapiro mark at msapiro.net
Thu Dec 6 01:36:16 CET 2007

Barry Finkel wrote:

>A few days ago in one of my Mailman 2.1.9 lists, a posting at 7AM
>was distributed to the members without problem.  The mail is addressed
>to two lists, and both lists received, archived, and distributed the
>At 5PM one of the recipients must have forwarded the mail back to
>the lists.  The RFC 822/2822 mail headers have the same
>     Return-Path:
>     From:
>     To:
>lines as the original mail, and in addition there is a header line
>     X-BeenThere: ...
>for one of the lists (i.e., the list to which this recipient is
>subscribed).  The mail reached Mailman.  I see in the Postfix
>     status=bounced (mail forwarding loop for LISTNAME)
>I assume this is because there already is an X-BeenThere line for that

I am confused about the Postfix log entry. The X-BeenThere: header is generated
by Mailman on outgoing mail and is checked by Mailman on incoming mail to
avoid reposting the same message to the same list. A message to a list with an
X-BeenThere: for that list will be discarded and logged as a discard in the
vette log.

Postfix should pay no attention to an X-BeenThere: header, but It may have
detected a loop on some other criteria.

>The mail to the other Mailman list was accepted by Mailman
>and redistributed to that list.  But I do not see a copy of the
>second distribution in the archives.  I can see why Mailman accepted
>the 5PM mail - it had an authorized "From:" address.  But why was
>the mail not archived?  Because it was a duplicate mail?

If you look in the archives/private/listname.mbox/listname.mbox for the list,
you will see both messages, but pipermail did not add it to the HTML archive
because of the duplicate Message-ID:.

>I would expect to have the archives contain a record of what was
>sent.  Should Mailman have caught the duplicate posting?

Other than X-BeenThere:, Mailman doesn't detect duplicates. It archived the
message as you will see from the archives/private/listname.mbox/listname.mbox
file, but pipermail did detect the duplicate Message-ID: and didn't add the
second copy to the same list's HTML archive.

>I have not been in contact with the recipient to determine exactly what
>he/she did.  I would like to prevent this from occurring in the future.

It's hard to know what happened, but I wouldn't be surprised if it were not
some brain dead MTA doing this. I have seen messages returned to me that
apparently got to some MTA that then decided to deliver a copy back to me
apparently because I was in a To: or Cc: header of the original.

Go to the archives/private/listname.mbox/listname.mbox file and find the second
message (or a copy of it if you have it) and look at the chain of Received:
headers for clues.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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