I installed and tested Mailman3. I imported a Mailman2 list. All looks good but I get this error.
Recipient address rejected: User unknown in virtual alias table; from=<hit@options.org> to=<atm@alist.net>
The aliases seem to show up find in the GUI for the control panel software I use. Postfix virual file has a mapping of atm to atm@alist.net .
It seems mailman at least sees the connection. From the smtp.log under mailman:
Mar 02 10:14:13 2023 (1242405) ('127.0.0.1', 56410) recip: atm@alist.net Mar 02 10:14:13 2023 (1242405) ('127.0.0.1', 56410) Data: b'DATA' Mar 02 10:14:13 2023 (1242405) ('127.0.0.1', 56410) Data: b'QUIT' Mar 02 10:14:13 2023 (1242405) ('127.0.0.1', 56410) connection lost Mar 02 10:14:13 2023 (1242405) Connection lost during _handle_client() Mar 02 10:53:13 2023 (1242405) Available AUTH mechanisms: LOGIN(builtin) PLAIN(builtin)