Mercury Mail Transport System - The Mercury Mail Transport System is a mail server that sends and receives messages on behalf of a...
Dovecot - Dovecot is an open source IMAP and POP3 email server for Linux/UNIX-like systems, written with...
hMail Server - hMailServer is a free e-mail server for Microsoft Windows.
Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
mailcow - An open source mailserver suite.
Courier IMAP - The Courier IMAP server is a fast, scalable, enterprise IMAP server that uses Maildirs.