I'm having problems sending emails to one specific domain (multiple users sending emails and they are returned). I have checked my Exchange server 5.5 and there are no blocked addresses in there besides the default local host. I have also checked my firewall and do not see them blocked. The error on return is as follows: The recipient was unavailable to take delivery of the message The MTS-ID of the original message is: c=US;a= ;p=My Company;l=EXCHANGE-040315161041Z-44509 MSEXCH:IMS:My Company:My Company:EXCHANGE 3499 (000B09AA) Host unreachable Thanks!!