Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
Geary - Geary is an email application built for GNOME 3.
Sendmail - Sendmail is a general purpose internetwork email routing facility that supports many kinds of...
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.