judging by the response from the tech, he is looking at the problem from the wrong end.
"alisonwachstein.com has no valid servers thus the message never gets out."
The problem they need to be looking at is not so much that the message never gets sent, but that the script, including theirs, goes to a 500 server error when an email address with a domain that does not exist is used.
that is the real problem.
the domains lack of existence should not result in a 500 server error.
It should not cause the SMTP server to stop responding. the SMTP Server should be able to step over the address and allow the script to move on to the next one.