Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
mailcow - An open source mailserver suite.
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
hMail Server - hMailServer is a free e-mail server for Microsoft Windows.
Sendmail - Sendmail is a general purpose internetwork email routing facility that supports many kinds of...
SmarterMail - SmarterMail is a next generation email management server that is offering several business collaboration and communication features as well.