Have you set Local Domains?.
Go to General>Properties>Local Domains and add your domain(s).
What is "Send/Receive"?
exchangelist@xxxxxxxxxxxxx on 7/25/2006 11:15 AM
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
<server_name.domain.com #4.0.0 smtp;450 Client host rejected: cannot find your hostname IP_address