How can I update Active Directory so that user mailboxes are updated to point to a recovery server that is hosting the mailbox database?

A. If an SCR target server is enabled as the host of a mailbox database, the user objects in AD need to be updated to point to the new database location on the SCR target server, SG, and database. Using PowerShell with the ConfigurationOnly switch, you can list all non-system mailboxes and update the object to point to the new location. The format would be

Get-Mailbox -Database (SCR source server)(SCR source SG)(SCR source mail database) |where {_.ObjectClass -NotMatch '(SystemAttendantMailbox|ExOleDbSystemMailbox)'}| Move-Mailbox -ConfigurationOnly -TargetDatabase (SCR target server)(SCR port SG)(SCR port mail database) -Confirm:$false

For example,

Get-Mailbox -Database savdalex01sg1mbx1 |where {_.ObjectClass -NotMatch '(SystemAttendantMailbox|ExOleDbSystemMailbox)'}| Move-Mailbox -ConfigurationOnly -TargetDatabase savdalexdrsg1portmbx1port -Confirm:$false

Once AD replication has completed, users will be redirected to the new home of their mailbox.