The SMTP relay settings for a script in a web site require that the sending address is a valid email account for the domain that the message is being sent from. Unfortunately, an alias email address will not work.
If you are sending through
then the from address needs to be validAccount@EXAMPLE.com
All web servers are white listed to the email servers and do not need SMTP Authentication.
The exception to this rule are CDONTS and BLAT.EXE which have pre-configured relay servers. Any sending address can be used in this case.