Hitashi mancho via Mailman-users writes:
> One of our users posted an email using a Bluemail Desktop client on one of
> the mailing lists. This email bounced with the reason "501 Message has
> defects".
Bouncing the message is arguably an overreaction to this particular
defect, but in fact Bluemail is violating a "MUST NOT" in RFC 2045.
Mailman takes the position that in principle we should not forward
non-conforming mail. At least one expert has told me he considers
this defect harmless, but (a) it's not clear to me that it is harmless
(especially in the hands of a malicious actor targeting carelessly-
written applications) and (b) it's hard to get excited about adding
complicated logic to the code to make life easier for an application
that doesn't conform to a trivial 30-year-old restriction.
> However, it gets accepted if the same user posts the same email
> on the same mailing list using Webmail (RoundCube) or Thunderbird.
I'm not familiar with the maintainers of RoundCube, but Thunderbird
has a long history of respect for Internet standards.
> There is nothing in mailman.log and bounce.log, even in debug mode.
Since this is happening during receipt of the message I would guess
that all messages related to the problem would be in Mailman's
smtp.log. I don't think you'd see anything about this in mailman.log
unless the defect managed to crash the lmtp runner or all of Mailman.
bounce.log reports bounces *received* by Mailman, not bounces caused
by Mailman.
> Apr 21 18:00:47 2025 (1979121) ('127.0.0.1', 44502) << b'501 Message has
> defects'
I seem to recall that Mark submitted a patch to add the defect list to
this message. I will follow up on that (although it doesn't help get
the message delivered to subscribers, it will make diagnosis a lot
easier and faster).
> Content-Type: multipart/alternative;
> boundary="----sinikael-?=_1-17452386441150.6962994414278503"
> Content-Transfer-Encoding: quoted-printable
This the problem. When Content-Type is 'multipart', the only values
allowed for Content-Transfer-Encoding are '7-bit', '8-bit' and 'binary'.
This is a "what were they thinking?!" level bug.
--
GNU Mailman consultant (installation, migration, customization)
Sirus Open Source https://www.siriusopensource.com/
Software systems consulting in Europe, North America, and Japan
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