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.
Halon MTA - Scriptable and scalable SMTP server and email framework designed for service providers.
mailsend-go - mailsend-go is a command line tool to send mail via SMTP protocol, written with golang.
KumoMTA - KumoMTA is the world's first Open-Source MTA designed from the ground-up for large-volume senders. Get a fast, flexible, supported solution.
sendEmail - sendEmail is a lightweight, command line SMTP email client.
MailerQ - MailerQ is a high performance Mail Transfer Agent (MTA) designed for delivering large volume email messages at very high speeds.