From a machine external to your network, open a command shell and type:
>telnet yourserveraddress 25
you'll see a prompt, type
>EHLO yourstationname
server details ensue, then type
>MAIL FROM:
iamspamming@hotmail.com
server acknowledges, then type
>RCPT TO:
bill@microsoft.com
if your machine is properly configured, you should see an error message .
If you see a prompt to process to the DATA phase, you're in trouble!
type QUIT to exit the session