A.Run the Set-DatabaseAvailabilityGroup cmdlet, and then enable Datacenter Activation Coordination for DAG1.
B.Run the Set-MailboxDatabase cmdlet, and then configure all mailbox database copies as lagged copies.
C.Run the Suspend-MailboxDatabaseCopy cmdlet, and then switch over all mailbox databases to Server2.
D.Run the Update-MailboxDatabaseCopy cmdlet, and then modify the mailbox database Activation preference.