Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
OpenSMTPD - OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with...
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
Dragonfly Mail Agent - A small Mail Transport Agent (MTA), designed for home and office use. Part of ...
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Exim - Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.