[Bug 558128] Re: remove 552 exception for SMTP perm/temp

Robert Mathews rob-launchpad.net at tigertech.com
Mon Oct 30 19:01:31 EDT 2017

I experienced a problem with Mailman 2.1.24 as a result of this.

A list received several large messages in one day that made the size of
a digest exceed 90 MB. When Mailman sent the digest, it got back this
SMTP error:

 552 5.3.4 Message size exceeds fixed limit

And logged this to logs/smtp-failure:

 SMTP session failure: 552, 5.3.4 Message size exceeds fixed limit,
msgid: <...

Unfortunately, the SMTPDirect.py code mentioned in this bug report
special-cases "552" errors to treat them like "452" errors, resulting in
Mailman trying to redeliver this message in an infinite loop until I
removed it from the queue.

The special-casing is apparently to work around a documentation error in
RFC 821 that was corrected in RFC 2821: The fear was that MTA authors
had followed the documentation error and were returning a 552 instead of
a 452 for the case of "too many recipients in this session".

I would expect that few-to-no mail servers in active use have such a
problem anymore; the original bug here requesting the removal of the
workaround code is 13 years old. At this point, it's very likely that
the workaround code merely makes Mailman wrongly retry legitimate 552
"Message size exceeds fixed limit" deliveries over and over.

The obsolete code should probably be removed. A trivial patch against
Mailman 2.1.25 is attached.

** Patch added: "mailman-bug-558128.patch"

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  remove 552 exception for SMTP perm/temp

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