[Mailman-Users] Problem with Micrososft Exchange 2003 SBS

Stephen J. Turnbull stephen at xemacs.org
Mon Oct 11 06:58:18 CEST 2004

>>>>> "Jan" == Jan Kellermann <jan.kellermann at werk21.de> writes:

    Jan> If this customer send a mail to two lists in to:-field,
    Jan> The problem is, that the M$-server deletes one mail because
    Jan> they have the same rcpt and message-id.

If they have the same Message-ID, they're the same mail.  RFC 2822

   In all cases, it is the meaning that the sender of the message
   wishes to convey (i.e., whether this is the same message or a
   different message) that determines whether or not the "Message-ID:"
   field changes, not any particular syntactic difference that appears
   (or does not appear) in the message.

In other words, generating the Message-ID to reflect your customer's
intent is the customer's responsibility.  The bug is not in Mailman,
and possibly not in MS Exchange.  Your customer is responsible for
generating appropriate Message-IDs, and/or delivering a single message
with multiple list recipients to multiple mail folders on receipt.

According to the RFC, Mailman (as an example; any other mailing list
distribution software would be the same) MUST NOT change the
Message-ID without explicit permission of the sender.  There is no way
that the Mailman project can distribute a Mailman that does such a
thing, and (unless this customer is your only customer using this
Mailman installation), you must not modify it to do so, either.

On the other hand, MS Exchange may be within its rights to delete the
mail.  (I would guess that if you look carefully at RFC 2821, the MTA
is not allowed to do this---in general, it's not supposed to pay
attention to the headers---but I don't know.[1])  However, you may wish
to point out to your customer that this is clearly open to abuse.
Someone who wants to embarrass an Exchange user can send an innocuous
message to that user's amilbox, then reuse the message ID with a
message that they wish to hide from the victim, making it look as the
the victim ignored the mischievous message.

    Jan> We are providing over 200 lists and have no problems at all.
    Jan> But this customers is sure, that this is a mailman-bug.
    Jan> I need support to argumentate. Is here anybody who is working
    Jan> with M$-exchange? Or is here anybody who can proof, that it
    Jan> should be no problem to have 2 mails with same rcpt and same
    Jan> msg-id?

As far as the RFCs are concerned, it's a single mail.  Mailman MUST
pass on the Message-ID as received; it has no way to determine the
intent of the sender.

Now, why argue?  As long as the sender really wants you to alter the
Message-IDs, the RFC doesn't prohibit it.  So I suggest you double
their fee, and give them what they want as a Custom Installation
Tailored To Their Advanced Mail System[tm].

Possible low-cost approach: Mailman will generate a message-ID if it's
not present in the message it receives.  So it's possible that all you
need to do is add Message-ID to the list of headers that Mailman
strips from received messages.  You may need to actually change the
Mailman code, depending on where stripping and ID generation are done,
but it should be trivial.  Of course, only do this for lists that are
used exclusively by this particular customer.

N.B.  I am not a lawyer nor a member of the IETF editorial board.

[1]  Since this is a Mailman list, I'm going to make no effort to
determine whether or not MS Exchange is broken.

Institute of Policy and Planning Sciences     http://turnbull.sk.t

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