I recently followed the instructions here https://github.com/g4rf/dockerized-mailcow-mailman, and was able to create a new Mailman 3, Debian-based installation. I then followed the instructions here https://docs.mailman3.org/en/latest/migration.html in order to migrate from my old, Centos-based installation, to the new, Debian-based installation. It seemed to work well, but unfortunately a problem showed up.
Whenever someone posted to one of the lists on the new installation, the messages were rejected by Postfix:
postfix-mailcow-1 | Aug 5 20:55:48 ef2b760c2e61 postfix/cleanup[8681]: B7B856099EC: message-id=<A8946B8E-2A47-4701-9548-4544981FAC5E@gmail.com> postfix-mailcow-1 | Aug 5 20:55:49 ef2b760c2e61 postfix/cleanup[8681]: B7B856099EC: milter-reject: END-OF-MESSAGE from unknown[172.22.1.1]: 5.7.1 This message does not meet our delivery requirements; from=<mylist-bounces@myserver.dk> to=<mylistuser1@gmail.com> proto=ESMTP helo=<[172.19.199.4]> postfix-mailcow-1 | Aug 5 20:55:50 ef2b760c2e61 postfix/cleanup[8681]: 216D36099EC: message-id=<A8946B8E-2A47-4701-9548-4544981FAC5E@gmail.com> postfix-mailcow-1 | Aug 5 20:55:50 ef2b760c2e61 postfix/cleanup[8681]: 216D36099EC: milter-reject: END-OF-MESSAGE from unknown[172.22.1.1]: 5.7.1 This message does not meet our delivery requirements; from=<mylist-bounces@myserver.dk> to=<mylistuser2@mail.dk> proto=ESMTP helo=<[172.19.199.4]>
So, for each of the existing lists, I had to delete the old list and create a new one - with the same name and the same users. After this, everything seems to work as expected.
Thanks for all the work you all has put into this, Jesper