I set up docker-mailserver[0] Monday in ~6 hours, most of which were me trying to be fancy using podman instead of docker and dealing with SELinux. But then again I did choose it over mail-in-a-box for just that level of customization. Obviously I can't tell how reliable it will be in the long run yet, but since it's using the classic Postfix/Dovecot stack I expect it'll be pretty stable

[0] https://github.com/docker-mailserver/docker-mailserver