Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
mailcow - An open source mailserver suite.
Eudora Internet Mail Server - Eudora Internet Mail Server is a highly advanced internet mail system that supports the all kind of email systems and clients either it is IMAP, POP3, SMTP and much more.
Roundcube - Web-based IMAP email client
WildDuck - Self hosted modern mail server