Have you actually tested it to see if it's an
open relay? Why do you think it's an open relay? You'll need to post some evidence to substantiate what you're saying (such as headers form some email)? What's happening to this email (is it in the queues or is it being sent out)? Have you checked to see if any of the accounts have been compromised? Have you searched the forums for some further information, this subject has been covered recently.