Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.

blat - Blat is a small, efficent SMTP command line mailer for Windows.

Sendmail - Sendmail is a general purpose internetwork email routing facility that supports many kinds of...

CMail - CMail is a free Windows command line mailer with advanced message formatting options.

Exim - Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.

mailsend-go - mailsend-go is a command line tool to send mail via SMTP protocol, written with golang.