This tool is a command-line interface for testing SMTP servers. It supports many protocol options and connection methods, including: plaintext SMTP, SMTP with SSL on connect (the deprecated method many clients use on port 465), STARTTLS after session start, SMTP AUTH with basic authentication or MD5-based methods, and more with good debugging output to help diagnose problems that can be difficult to find using most full-featured e-mail clients that lack good feedback on the outgoing process.