In Exchange Management Console, Organization Configturation, Hub Transport, Remote Domains; There are two domains:Name DomainXXXX *Default *For some reason, both of them are default.Since there are two default domains, I cannot set up Internet Message format properly.When I remove XXXX, it gives error message "The default remote domain cannot be removed".If I used the Exchange Management Shell, enter "Remove-RemoteDomain -Identity "XXXX', after enter Y to confirm the remove operation. I receive the same error message.The Set-RemoteDomain shell command does not allow me to change the default domain option.The problem was came from when we were using Exchange 2003. By mistake, we added anXXXX domain in Exchange System Manager, Global Settings,Internet Message Formats. After we migrate it to Exchange 2007 Server, both XXXX and Default domains become default domain.

We can delete the remote domain via ADSI Editor: a. Launch ADSI Editor b. Expand Configuration->CN=Configuration,DC=domain,DC=com->CN=Services->CN=Microsoft Exchange->CN=Orgname->CN=Global Settings->CN=Internet Message Formats c. In the right-pane, find the entry of the remote domain and remove it d. Refresh the EMC, we can see the extra remote domain has gone

Thank you so much,your solution is excellent. The problem is resolved.

J Glad it works for you