SMTP Server Connection Diagnostics Tool

This free utility will enable you to troubleshoot SMTP Server issues much more easily than using telnet. It supports both open and SSL connections and contains a built-in library of commands such as EHLO, DATA, RCPT TO, etc...

The SMTP Console enables you to connect to SMTP Servers and step through transactions with our without SSL.

Lightweight, just an exe. Requires Windows and .Net Framework 2.0 or greater. Free to download, free to use.