I installed a brand new SBS2008 (w/ Exchange2007) server into a client network that had no server before; they had been POPing their e-mail. I set up Exchange, and all PCs/users work just fine, except for ONE user gets messages rejected from their OWN server when he tries to send e-mail..Now, this only happens intermittently, but here's the error he receives:
"You are not allowed to send this message because you are trying to send on behalf of another sender without permission to do so. Please verify that you are sending on behalf of the correct sender, or ask your system administrator to help you get the required permission."
Now, let me emphasize that he is NOT trying to send on behalf of another user, nor is he a delegate of another mailbox/account. Again, this will happen for several hours, and then the problem will go away altogether for 1-2 days, or whatever, then it will return.
BUT, when he uses OWA, he never has this issue, which led me to believe that his Outlook profile was corrupted. As you would expect, I trashed his OL2007 profile and created a new profile, and 1 day later, he had the EXACT same problem. Again, he is the only person having this problem, and ALL other mailboxes/Outlook accounts are behaving fine and get no errors. ONE other user had the same problem within 1 day of the guy still having issues today, but I built a new Outlook profile for him, and that guy hasn't had the problem since.
My client is frustrated, and *I* am frustrated, since I cannot find a damn solution to this quandary!
Can you please HELP!!