This is an Orphan Mailbox.
The way it works is there are two levels of orphaning:
1. Messages that are not associated with a mailbox. (the messages are added to a new mailbox)
- No reference to MailboxMessage table.
2. Messages that are associated with a mailbox but are not associated with a folder. (a hidden folder is created in the mailbox called _Orphans)
- No reference to MessageFolder table.
You can assign your account to the mailbox and then be able to search it. You can also delete messages from that mailbox if you like.
For the _Orphans mailbox, a delete policy can be applied to just that mailbox, causing the messages to be removed.
For the _Orphans folders, the items will show up in search results and can be tagged for deletion, or standard policies can be created to remove over time.
Note: Do not be alarmed over orphan messages, we simply put them in this folder because going forward Archive Manager is using the MailboxMessage table for security and MessageFolder for ownership.