Docker Mailserver (DMS) is an open-source production-ready full stack mail server that you can self-host in a Docker container
This is a simple containerised mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.). Only configuration files, no SQL database. Easy to deploy and upgrade. I see it is often recommended to others, as I noticed in a Lemmy forum today.
It is receiving regular updates and has quite extensive documentation. It has over 11,000 likes on Github.