We are looking to move the mailboxes from an on-premise Exchange 2010 server hosted at a child company to our Exchange 2013 server using a cross forest migration.
I have setup a two way forest trust and have successfully migrated a couple test mailboxes however I'm encountering a problem.
When I move firstname.lastname@example.org to the new exchange server, user1 is not able to email anybody who's mailbox is still waiting to be transferred and visa-versa. In other words, email@example.com (now hosted on Exchange 2013) cannot send an email to firstname.lastname@example.org (who's mailbox is still waiting to be transferred).
The goal in the near future is to decommission the Exchange 2010 server altogether however for a period, both servers will need to coexist while the mailboxes are being moved.
Is there a way for Exchange 2010 to redirect email that has been sent to a mailbox now hosted on Exchange 2013?