We were getting the following error after a migration to Exchange 2010 from 2003 which indicated that Exchange was still looking for the old server.
Event: Microsoft Exchange cannot find a route to the source transport server or home MTA server
The problem is during the migration the old server didn’t get pulled from Active Directory correctly so there were still settings that caused Exchange to believe that there was another MTA available.
To resolve we opened up ADSI Edit on the AD server and navigated to the following container:
Inside this container you may find entries that reference your old server. Just delete them and you should be good.