Originally Posted by
moxquito
Good point...
however mail is received into a domain via POP from an SMTP server, so my original statement still stands unless you are authorized on the domain to send mail, either by way of IP from the domain or authenticated by some other means, you will not be able to connect to the SMTP server to send mail.
try randomly connecting to any SMTP server not on your domain and see if you can. If you find one the domain is open for relay. I guarantee you will not find many if any.