There is a setting in Outlook Options that automatically empties the Deleted Items folder when you exit Outlook. Here's how to prevent this:
Step One: Click the File tab.
Step Two: Click Options and then click Advanced.
Step Three: Under Outlook start and exit, clear the Empty Deleted Items folders when exiting Outlook check box.
Step Four: Click OK to save the change.
Use the Search Deleted Items box (or press CTRL + E) to find the item you want to recover.
To find other types of items, such as deleted appointments, contacts, or tasks, sort by the Icon column.
If you know the approximate date when you deleted an item, add the Modified column to the Deleted Items folder view. H
You can sort by the Modified column to group items deleted on a specific date. This is a good way to find messages from a deleted folder because they would all have the same modified date.
Step One: On the View tab, in the Current View group, click View Settings.
Step Two: Click Columns.
Step Three: In the drop down list under Select available columns from, select Date/Time fields.
Step Four: Select Modified and then click Add. If you want, you can change the order that the columns appear.
Step Five: When you're finished, click OK.
Your admin may have set up a policy to delete items from your Deleted Items folder after a certain number of days. Just like when you deleted an item, items deleted by a policy are moved to the Recoverable Items folder. So if you can't find something in your Deleted Items folder, look for it in the Recoverable Items folder.