For the past few months, we have been running a hybrid Exchange 2013 environment, and successfully migrated all student mailboxes to Exchange Online.

With the summer holidays approaching, we are looking to complete the process, and move all staff mailboxes over to Exchange Online, in what will be a cutover migration.

Having read through a couple of posts about similar scenarios, most suggest;

-          - First removing the users (whose mailboxes will be migrated), from Office 365, AFTER disabling DirSync on premises. These users in Office 365 currently dont have assigned Exchange Online licences.

-          - Re-enable DirSync following the cutover.

My question is, for student mailboxes which were migrated over earlier in the year, how are these affected following the cutover? Obviously students wont be included within the cutover batch, but these accounts still show in our on-premises EAC. A cutover migration allows for us to decommission our on-premises Exchange servers, but surely this would affect the visible student mailboxes. Is there another final step we need to complete, to permanently disassociate the mailboxes from our on-prem mail server? (was thinking routing addresses and the like)

Also, the step of disabling DirSync is this enough, or does it need to be removed? Should it be disabled prior to removing the synchronised members of staff from Office 365?

How do we tear down our hybrid setup following the cutover?

Lots of questions Im afraid.

Many thanks.

• Edited by MR JH 20 hours 9 minutes ago addition