Excluding Inactive Mailboxes from Org-Wide Retention Holds
Exchange Online supports inactive mailboxes as a way to keep mailbox data online after Office 365 accounts are removed. Inactive mailboxes are available as long as a hold exists on them. You can update mailbox properties to exclude all or some org-wide holds. If you exclude holds from a mailbox, you run the risk that Exchange will permanently remove the mailbox. If that’s what you want, all is well, but if it’s not, then you might not be so happy.