Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
msmtp - msmtp is an SMTP client.
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
OpenSMTPD - OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with...
Exim - Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.
sendEmail - sendEmail is a lightweight, command line SMTP email client.