Hi Kate,
When a user deletes messages from their Deleted Items folder or uses Shift+Delete to permanently delete a mailbox item, the deleted items are copied to a hidden folder in the user’s mailbox. This folder is called “Recoverable Items”. Items in the “Recoverable Items” folder are retained for 14 days by default and then purged by Microsoft Exchange.
If you can’t find any items using Recover Deleted Items,I am afraid that the data has loosen permanently.
Thanks,
Jacky Ding