Profile unix updating user
If you notice any differences with the way MS is handling mailboxes of a deleted user as you read this please leave a comment and I will update the answer.) I'll only cover the options within the scope of the administrative options of Office 365 itself.If you have 3rd party offerings or solutions in place you'll need to contact them for assistance.If you are outside the retention period, you cannot recover the deleted mailbox...
Also, the usermod command will often fail, especially on Raspbian 8 (Jessie), with the error message “usermod: user pi is currently used by process“. You should select a different name of your own choosing.
Inactive mailboxes can't receive email and aren't displayed in your organization's shared address book or other lists.
IMPORTANT: Make sure the hold is in place BEFORE deleting the mailbox.
The contents of an inactive mailbox are preserved indefinitely.
This allows administrators, compliance officers, or records managers to use the In-Place e Discovery feature in Exchange Online to access and search the contents of an inactive mailbox.