I am preparing a migration from one domain in forest A to a new domain in forest B. I have an Exchange 2003 server in A and a new Exchange 2007 server in B. I have SMTP addresses in forest A with two different namespaces (let's call them abc.com and xyz.com).
Forest A's domain is actually abc.com, xyz.com is another namespace we use because it is shorter and has always been around so I need to properly deliver to both abc.com and xyz.com. This works well in the current configuration.
When I create a test user in my new forest B (let's call this mno.ad), I can deliver mail to abc.com but not xyz.com. Let me back up a bit. I have the old server configured to deliver all internal mail to the new server which cannot be resolved in its namespace. This lets me send to abc.com or xyz.com, hit the old server, when a user isn't found, it forwards to the new server and delivers. The way back is where things break down. For some reason, even though I have abc.com and xyz.com set up as internal relay domains, I can only deliver to abc.com (the one that matches my old ad name). I belive this is because abc.com is configured in the new DNS as a stub zone pointing back to my old abc.com domain controllers. The xyz.com namespace (on the new side) is configured as a primary zone. I am guessing the new mail server is searching the global catalog and finding my users on the old server and suceeding but I am not sure how to get the other namespace delivering.
I want to move a few mailboxes a week ahead of time to work out any bugs before I make the change to move all user accounts and workstations into the new domain. I don't want to sort out mail routing issues when I have all of these other issues to work out.
I have a kind of strange scenario so feel free to ask more detailed questions and I will answer to the best of my ability.