Package smtpd implements an SMTP server in golang.

• STARTTLS (using crypto/tls)
• Authentication (PLAIN/LOGIN, only after STARTTLS)
• XCLIENT and PROXY protocol (for running behind a proxy)
• Connection, HELO, sender and recipient checks for rejecting e-mails using callbacks
• Configurable limits for: connection count, message size and recipient count
• Hands incoming e-mail off to a configured callback function

The package is tagged with semantic version numbers, making it suitable for use in a Go Module.

If you end up using this package or have any feedback, I'd very much like to hear about it. You can reach me by email.