Dovecot - Dovecot is an open source IMAP and POP3 email server for Linux/UNIX-like systems, written with...
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Cyrus IMAP - The Cyrus IMAP server differs from other IMAP server implementations in that it is generally...
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.
DBMail - DBMail is a fast, scalable IMAP4 and POP3 server that stores all email and users in a Postgresql...
mailcow - An open source mailserver suite.