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Message sizes exceeding limits after migrating from Exim to Postfix
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Description

Since July 2024, we've had users reporting receiving this message when attempting to send emails with attachments smaller than 25MB:

The response from the remote server was:

552 5.3.4 Message size exceeds fixed limit

The recipients for the emails being blocked are both Google groups and GMail mailboxes in our domain, both from @wikimedia.org and external senders. As a workaround, folks are able to add files to Google Drive and share those links.
Prior to his departure, Nick confirmed that our default attachment size limit is 25MB in Google Admin console, without any further ability to increase this limit (see this Google knowledge article.)
Based on our investigation of the bounceback message IDs and other resources, it seems like there may be a mail server issue - possibly some global limit on message and/or attachment size?

Message IDs:
672ea76a.050a0220.1482da.e318.GMR@mx.google.com
672e7062.a70a0220.334423.6497.GMR@mx.google.com
66a3e4a9.5d0a0220.18999.0809.GMR@mx.google.com
668592d8.2e0a0220.1e749.657c.GMR@mx.google.com
66f6c8a3.050a0220.1d38b9.5bd6.GMR@mx.google.com

Details

Related Changes in Gerrit:
SubjectRepoBranchLines +/-
postfix: increase message size limit from 10MiB to 50MiBoperations/puppetproduction+3 -0
Customize query in gerrit

Event Timeline

DSeyfert_WMF created this task.Jan 8 2025, 8:17 PM
Restricted Application added a subscriber: Aklapper. · View Herald TranscriptJan 8 2025, 8:17 PM
Aklapper added a project: Mail.Jan 9 2025, 7:42 AM
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RhinosF1 subscribed.Jan 9 2025, 7:49 AM
MoritzMuehlenhoff subscribed.Jan 13 2025, 3:56 PM
gerritbot added a comment.Jan 13 2025, 10:36 PM

Change #1110873 had a related patch set uploaded (by JHathaway; author: JHathaway):

[operations/puppet@production] postfix: increase message size limit from 10MiB to 50MiB

https://gerrit.wikimedia.org/r/1110873

gerritbot added a project: Patch-For-Review.Jan 13 2025, 10:36 PM
gerritbot added a comment.Jan 14 2025, 7:53 PM

Change #1110873 merged by JHathaway:

[operations/puppet@production] postfix: increase message size limit from 10MiB to 50MiB

https://gerrit.wikimedia.org/r/1110873

jhathaway claimed this task.Jan 14 2025, 8:04 PM
jhathaway closed this task as Resolved.Jan 14 2025, 8:08 PM

@DSeyfert_WMF this appears to be a regression in our mail servers when migrating from Exim to Postfix. Exim had a default message size limit of 50MiB, but because we did not explicitly set the value, it was not carried over to the Postfix configuration. Postfix's default is lower, 10MiB, I have now raised the total message size limit to 50MiB, which is inline with the gmail default. Postfix does not offer a per attachment limit, so messages with attachments larger than 25MiB will be rejected by gmail, rather than Postfix. After this change I was able to successfully test sending a 21MiB message.

Maintenance_bot removed a project: Patch-For-Review.Jan 14 2025, 8:30 PM
Aklapper renamed this task from Message sizes exceeding limits to Message sizes exceeding limits after migrating from Exim to Postfix.Jan 15 2025, 5:03 AM
DSeyfert_WMF added a comment.Jan 15 2025, 3:08 PM

Thank you @jhathaway - initial tests from end users look good, thank you for your help resolving this!

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