In a nutshell: We are running Exchange 2010, our internal domain is a namespace that we do not own and therefore cannot by certs for. I brought up another new domain (that we own) and have built another Exchange 2010 environment that will obviously handle mail for the same domains. I'm looking to do a department by department migration instead of one fell swoop. I'm looking at different Exchange migration tools that will help. I need some sort of syncronization going between the two Exchange servers.
I have a CISCO Ironport and I figured out how to deliver mail to both Exchange servers if needed. In testing I found that after I migrate a user they can't email anyone else in the local domain that has not yet migrated because the Exchange server sees that message and realizes it routes mail for that domain and sends an NDR because the account does not exist on the new server yet. If it did exist on the new server it would deliver however the user would not get it because their outlook ( and computer) is configured to the old.
I you can see my deliema now, has anyone else tried this before?