ok, we have 2 exchange servers running in the same forest, one a 2007 and one a newly installed 2010, they are both authoritive for different domains. The domain that is going to be on the 2010 exchange already has a 3rd party email system in place for the time being until we can get everything migrated over. Right now when a user on the 2007 exchange box emails a user that will be on the 2010 but currently on the 3rd party, My question is 2 fold, If i remove all the users that are on the 3rd party from exchange, and remove the accepted domain that is currently being used by the 3rd party, will the 2007 exchange server just send out through inet like normal? or if i just remove the accepted domain and leave the users until i'm ready? Or is something like shared smtp namespace with an internal routing domain the way to go?