Piet Barber via Mailman-users writes:
this mailman3.service file seems to work better than the one on the mailman website: ( https://docs.list.org/en/latest/install/virtualenv.html#setup-virtualenv ) Thanks to "oneshot" !
Glad that works for you.
I recommend trying without the two "restart" lines. I suspect that what was happening is that systemd was waiting for something from Mailman that never occurred (possibly the PID file? but that should show up in much less than 30s!), timed out, and I don't have a clue what systemd would do about that, except try to restart (assuming Mailman shutdown? or after running "mailman stop"?) Those lines are specific to Mailman installations using MySQL-family databases, but you appear to be using PostgreSQL, which doesn't need them.
-- GNU Mailman consultant (installation, migration, customization) Sirius Open Source https://www.siriusopensource.com/ Software systems consulting in Europe, North America, and Japan