CMail is a command line e-mail sending tool. It was originally developed to assist with testing mail server and content analysis software. As a result, CMail provides many more message formatting and SMTP session control options than similar software.
blat - Blat is a small, efficent SMTP command line mailer for Windows.
mailsend-go - mailsend-go is a command line tool to send mail via SMTP protocol, written with golang.
Mailer - Free utility to send emails from the command line. No Installation. All contained in one file.
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
MailerQ - MailerQ is a high performance Mail Transfer Agent (MTA) designed for delivering large volume email messages at very high speeds.
msmtp - msmtp is an SMTP client.