Migrating AD account and not the exchange mailbox

Here is our setup.  We have 2 Forests.  We have the cross forest communication setup.  We have exchange on both forest.  Forest A ,Child A , and Exchange A.  Forest B, Child B, and Exchange B.  The users are going to be migrated from A to B.  The team in charge of the migration decided with upper management to not migrate the users mailbox but only the AD account portion.  I think this will cause issues with the users mailbox.
Is it possible to provide information if doing this type of migration will cause issues for the users email or if this is a valid migration process.
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Will SzymkowskiSenior Solution ArchitectCommented:
As long as you migrated the Active Directory Account and ensure that sidHistory is enabled once the user has been migrated to the new domain it will use it's sidHistory to access the mailbox in Domain A. The issue happens when the user has been moved to domain B and wants to use the new SMTP domain for domain B rather than domain A. At this point you will need to migrate the mailbox.

Take a look at the below link which describes in more detail sidHistory and Exchange (very old link but concept still applies)

Cross Forest Mailbox Migration for Exchange


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