Comment 1 for bug 1885172

So the posted message is in the archive, but was not received by whom? By no list members on only by some?

You need to check Mailman's logs and queues and possibly the MTA logs. Possibilities include the message is still in the out queue indicating an issue with OutgoingRunner or the message is in the shunt queue in which case there will be an exception and traceback logged in Mailman's error log.

See sections 6.2, 7, 8 and 9 at https://wiki.list.org/x/4030723 for more information.