Sending email with Telnet using SMTP commands is an easy way to test your SMTP server solution, sometimes however you need to authenticate yourself to the SMTP server, or your relay server needs to authenticate itself to the onward SMTP server, here’s a nice link which explains how to do it.

If you’re using Windows, you can use the Telnet application, if you’re using a Mac you can use Terminal, once Terminal is running, run the telnet command as normal e.g.

telnet servername port-number