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

Maileroo - Maileroo is a powerful email delivery platform, featuring a user-friendly SMTP service and Email API. It specializes in supporting transactional emails with advanced features like delivery tracking, as well as detailed open and click monitoring.

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

Postmark Express - What happens to your emails after you hit the "send" button?

sendEmail - sendEmail is a lightweight, command line SMTP email client.

Warmup Inbox - Warmup Inbox is a tool that automates the process of warming up your email inboxes, raising your sender reputation and inbox health automatically.