We have a user who can't receive emails to her Inbox from outside users when they use her primary email address. Her secondary email address works fine. I spoke to Websense about it and they narrowed it down to the IP address of one of our EDGE servers. The error message is SMTP 550 5.1.1 User unknown.
The EDGE server is Windows 2003 R2 64-bit. Exchange 2007 Service Pack 2.