Le 02/10/2022 à 06:35, Sébastien Riccio a écrit :
Hi,
After reading a bit the code and trying to understand it, here is what
I think happens here:
Given a bogus Message-ID, for example (notice it's missing angle
brackets < >:
Message-ID:
1883biz_pay_after_purchase:0:0_572392900$ae7ed6e4d53b424c84aaf83b30c507e7
Dovecot is parsing Message-ID headers and is looking for the angle
bracket as the begining of the Message-ID:
https://github.com/dovecot/core/blob/d2ff32792ac052610cea7d65f30de1ee139cb55c/src/lib-mail/message-id.c#L75
As none is found it will act as if there was no Message-ID header in
the mail (even that the header is present).
Then, pigeonhole's redirect function is told to generate a new
Message-ID if none was previously detected:
https://github.com/dovecot/pigeonhole/blob/5a3f4bd672cc2fb9e755a4b09c4753ac86e15f99/src/lib-sieve/cmd-redirect.c#L569
The result is the mail being forwarded, in this case, is now having
dual Message-ID and is not RFC 5322 compliant anymore and can be
rejected for this reason (hi, gmail?)
https://www.spamresource.com/2022/08/gmail-weird-rfc-5322-bounces-and-what.html
Some thoughts:
- First, to be honest, I'm not sure gmail would accept the original
mail with the bogus Message-ID sent directly to their servers, but if
it was refused, I would assume that these senders would have fixed the
issue on their side so their message are delivered (unless there is
some whitelisting going on?)
- What options could we have to resolve this?
a) Having dovecot core to remove the Message-ID header line from the
mail if it is not going to consider it valid ? (So there is no dupe
headers when pigeonhole adds one?)
b) Having pigeonhole check, when adding a new valid Message-ID, if
there is already one existing, and remove the bogus one ?
Hello,
In my opinion, an option c) should be considered.
Bogus or not, if a Message-ID is present in the header you should not
touch it.
For it own use, dovecot should continue to not use it as it is bogus.The
only thing to do is to warn in logs in the dovecot core.
In a forwarding scenario, you should not alter the existing Message-ID,
you should not take the responsibility to fix someone else problem.
The bogus message ID key is ok for duplicate detection. The only risk is
false trigger by another equal bogus Message-ID header. Bogus messages
are bogus so ...
For the present case, it means that the check for the header presence
should be done by pigeonhole directly, not relying on the dovecot core
Message-ID validity check.
In the missing/not implemented/not drafted redirect-as-new (inline or
attached) case which exiting in some systems, you will generate a
completely new message with a fresh/compliant Message-ID.
Emmanuel.
