All I would do is give them a ring and tell them that your board sends out mail to users (passwords, etc) and that when it attempts to do this, it gets a 'relay denied' message (you can even tell them that its SMTP error 553). Hopefully, if they have half a brain, they will know what you're talking about and can help!
We do have some articles online that may help your host if, for some odd reason, they don't have a clue <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
If you need even more details, you can post back to our ticket.
Thanks!
http://ubbcentral.com/support/faqs.php?product=UBB.classic#52
