This issue could be due to the retention policies but this could also be caused by litigation hold, eDiscovery case hold. Before proceeding verify the quota is exceeding by running… Read more »
Make sure Orphan mailbox is not listed under additional account. Also, make sure the same mailbox is not listed under Outlook > File > Account Settings > More Settings… Read more »
There are situations were the folder might have been deleted and may be moved inside any other folders available in the mailbox. In such case we may require to audit… Read more »