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"Uncaught bounce notification" from Yahoo and AOL
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I'm an administrator for the Wikimedians in Colorado mailing list, hosted on Over the last couple of months, we've been getting a lot of "Uncaught bounce notification" e-mails from Mailman whenever any e-mail is sent to our group (I've attached one of these e-mails to this issue). According to the error message in this e-mail, "either the bounce format was not recognized, or no member addresses could be extracted from it". I think this means that Yahoo and AOL changed their bounce message format at some point, and as a result e-mails sent to addresses that are no longer active (likely because they were set up by spammers in the first place) are being bounced, but Mailman doesn't know which user to unsubscribe as a result of the bounce. So far, I've been manually deleting these users from the mailing list myself, but it's getting to be too many to do by hand.

Is there any way for us to configure bounce message detection ourselves -- by providing a regular expression for these Yahoo/AOL bounce messages, say? If not, would it be possible for the system administrators of to configure this for us? Are there any configuration options you can suggest to help with this? If we can't find any other solution, we'll need to turn off bounce_unrecognized_goes_to_list_owner, which means that will keep spamming Yahoo and AOL's servers for users that no longer exist on their system.

Related to T232417, but that issue covers Yahoo temporarily rejecting e-mails, which this is about bounces that Mailman cannot parse correctly.

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There are bounce processing options mentioned on in case you want to fiddle. :)

Is there any way for us to configure bounce message detection ourselves

I really don't see any useful configuration other than providing a patch to the upstream mailman project or reporting it to Yahoo/AOL.

Maybe the 3.3 upgrade would detect those? T52864

While the manual says you normally should not touch the bouncing options, I would support you turning bounce_unrecognized_goes_to_list_owner off if the volume is high. I personally don't have a better suggestion, but maybe someone else can come up with a better solution?

jcrespo triaged this task as Medium priority.Jul 8 2020, 10:04 AM
jcrespo moved this task from Backlog to Mailman v3 on the Wikimedia-Mailing-lists board.
jcrespo moved this task from Mailman v3 to General on the Wikimedia-Mailing-lists board.