We recently performed a migration from an Exchange 2013 farm to Exchange Online, hosted in Office365. The migration method used was cutover migration.
There were roughly 190 users and cca. 400 mailboxes to be cloud synced.
Everything went ok until the moment when we needed to assign licenses to users (of course after Azure AD connect tool finished its duty).
When a cutover migration happens, it copies fully and then incrementally all the mailboxes from on-premises to Office365 and also it creates the users in Azure AD. Well, when the users are created, they are also mapped either as User Principal Names on one or more mailboxes or they are delegated to open certain mailboxes, exactly as they are set in on-premises.
Also, an Office365 user license is assigned to the respective users.
Should you decide that the assigned license is not the right one for the users, don’t remove the license and assign a new license, but rather replace the users` licenses with another one.
As soon as an user doesn’t have anymore a license that grants access to Exchange Online, all the mailboxes he used to have access to, will be tombstone-deleted.
Assigning back an Exchange online compatible license to an user is restoring only it’s main mailbox, in a best effort from Microsoft. Not all the mailboxes the user has had access to.
So don’t forget: always replace a license, don’t retract one to set another one.
See you later,