Non-unique Message ID in mail messages

[Daniel Ryšlink]

Hello!

I apologize for bringing perhaps trivial/well-known matter, but I am 
interested in your opinion.

RFC 5322 clearly states that mail messages SHOULD contain a Message ID 
identifier, but if the do contain it, it MUST be globally unique.

Despite this requirement, I have encountered senders (namely Spamcop) 
that sends obviously different (albeit related) messages called "Alert" 
and "Summary" (they are always related to the same incident and have the 
same Message ID). This creates all sorts of problems when processing 
these mails, namely with users that have local forwards from one domain 
to another (our mailserver hosts multiple domains), because for example 
Dovecot refuses to forward the second message, flagging it as a duplicate.

My question to you is - did you also encounter similar incorrect 
(according to RFC standards) problem, and if so, is there a way to 
persuade dovecot to perhaps determine the uniqueness of a message by 
other means than just checking the message ID (i.e. look at other 
identifiers, Subject, perhaps)? Because according to the log records, 
Spamcop does not seem to be the only offender.

Thanks in advance for any reactions, and if I did something wrong by 
writing this message, I apologize again in advance.

If required, I can provide samples of the Spamcop messages.

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--== Best Regards! ==--
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Daniel Ryšlink
Sysadmin @ Quantcom.cz
Czech Republic