We use Exchange Online (O365) in our organization.
There is a quite huge mailbox (thee digit GB) in our tenant which belogs to an AD object we shall call user A. For reasons which are hard to explain and IMHO don't matter here, we will have to deleted the user A AD object and want user B to become the owner of this mailbox.
I was told this wasn't possible or we would have to bring that mailbox back on-premise first (a bit hard, given its size), perform the user change there, then migrate it again to the cloud.
Could someone explain why this seems to be so difficult / complicated to do it straight in the cloud?
Looking at my AD, I would assume that the attribute "Mailbox GUID" is what ties the mailbox to an AD object. Why can't I just delete that attribute on user A in our AD and add it to user B?