So here’s a quick list of commands that will test an SMTP connection. The first thing to do is to make sure that you have used “Run as” to start the command window. Then type;
[server name] 25
helo [server name]
Some sort of random text you want to see in the email body …
Here’s the test output;
|Telnet/SMTP Sample Output|
The most common errors you'll get a relay failure - if you want to fix this you just need to make sure the "from" email address is internal to the organisation hosting the SMTP server (for example use Gmail accounts if using Google's SMTP server, etc).