dovecot
mailcow: dockerized
https://mailcow.email/
mailcow: dockerized is an open source groupware/email suite based on docker.
mailcow relies on many well known and long used components, which in combination result in an all around carefree email server.
docker-mailserver
https://github.com/docker-mailserver/docker-mailserver
Production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.) running inside a container. Only configuration files, no SQL database. Keep it simple and versioned. Easy to deploy and upgrade. Documentation via MkDocs.