database connection error crashes mailer service

[TheJJ]

when the DB is not there due to restarts, the mailer service crashes and has no proper recovery, except restarts from systemd that did reach the restart limit.

[sleepy-nols]

I think this could be fixed with using Requires instead of After (or both) in the mailer service with postgresql. Then the mailer service should not be started until postgres is up.
https://serverfault.com/questions/812584/in-systemd-whats-the-difference-between-after-and-requires