Hi, I have a 2 node Exchange 2013 DAG running CU5 that is having problems and have built 3 new servers to replace the 2.  We will create a new DAG.  Yesterday I installed Exchange 2013 with CU8 and the install completed successfully with no issues. I have a mailbox on the new server that I can connect to using OWA and send mail with no issues.  When I send mail to the mailbox on the new server, the message hangs on either of the existing servers in the Unreachable Domain queue with the error that "There is currently no route to the mailbox database."

Troubleshooting to this point:

Restart Transport service on server1 and server2
Matched configuration for receive connectors between server3 and the other 2.
Messages sent from server3 to a mailbox on server1 or server2 is delivered fine.
Replies and messages sent from server1 or server2 to a mailbox on server3 are not delivered.

What am I missing?

If all servers are in the same organization, I probably wouldn't create a new DAG.  I would join the new machines to the new DAG and create database copies because it's probably easier than moving mailboxes.

When you look at the details of the queued message, are there any clues?