I have been tasked with merging Exchange infrastructure with Company A and recently bought Company B. From my research I think I understand what needs to be done, but I wanted to double check.
For starters, Company A and Company B will continue to use their respective domains for logging in. So we create a Active Directory Trust between DomainA and DomainB, and then a Exchange Forest Trust between DomainAXCHG and DomainBXCHG. (simplified there of course)
After that, is it possible to migrate a mailbox from DomainBXCHG to DomainAXCHG, and let them continue to log into their mailbox using their DomainB credentials? I know we did mailbox migrations from our old Exchange 2007 server to our new Exchange 2010 server, but that was on the same domain. Across domains is unclear and I don't have a lab environment set up to test it.
Some of what I have read (at least for alternatives) seems to lead that you have to create an account & Mailbox in DomainA, and then give their account in DomainB access to that mailbox. But that would mean exporting their email into a .pst and importing it into the new mailbox though.