I just finished my install of Exchange 2010 today and after jumping through many hoops of fire to get the software installed I have an issue. I migrated 2 test users from our 2003 exchange server and after the migration was complete I sent the users a few email messages from a mailbox on the 2003 server. The messages never got to the 2010 exchange mailboxs, and seem to be in the Queue listed as "Messages with an unreachable destination". Also when sending from the 2010 mailbox, the messages never arrive on the 2003 users mailbox. So there seems to be some sort of routing issue. Any ideas would be helpful.