I know there's been plenty posted on this topic, but none seems to hit exactly what I'm trying to do. We've recently acquired another organization who is running an Ex 2003 server for DomainA.com. Our organization is running DomainB.com on Exchange 2010. We would like to move DomainA.com to our Exchange 2010 server through a slow migration (one account at a time). New user accounts have been created for all DomainB users in DomainA.
Here's the process I'm planning to do along with the missing pieces I need help with
1. Establish trust relationship between servers in DomainA and DomainB
2. Add DomainA.com as an Internal Relay domain on our Exchange 2010 server. Define a Send Connector for the domain to route emails to the Exchange 2003 server.
3. Move a user account from DomainA to DomainB using a combination of Prepare-MoveRequest.ps1 and New-MoveRequest (this has been tested successfully using this technique
4. Once the mailbox has moved from DomainA to DomainB, delete the user account and reassign the mailbox to the new DomainB user account using this technique
Now, the missing pieces
1. Email will still be delivered to the DomainA.com (Exchange 2003) email server until more than 50% of the accounts are moved to DomainB. How do I configure Exchange 2003 to relay mail for the moved accounts to our Exchange 2010 server? I know very little about Exchange 2003.
2. If I change the MX record for DomainA.com to point to our Exchange 2010 email server, would the send connector relay emails for the DomainA.com accounts we have yet to move from DomainA to the old Exchange 2003 server? So, can I host accounts for DomainA.com on Exchange 2010, and say "if you don't find the account here, send it to the old email server over there."
3. This seems the "cleanest" way to do this slow migration - however, if you know something easier, I'm all ears!