Recovering Deleted Email Messages
When you delete an email message, it will be filed in the “Deleted Items” folder. If you delete a message from the “Deleted Items” folder, it can still be recovered for 30 days (it gets held in a recovery area).
In the past, some email software bypassed filing deleted messages in the “Deleted Items” folder and sent it straight to the recovery area. A similar behaviour can be seen if you have configured Outlook to empty the “Deleted Items” folder upon Exit (under Options-Advanced)
To find messages that have been deleted but no longer appear in the Deleted Items folder
In Outlook
Select the Deleted Items folder
In the ribbon at the top click on the “Recover Deleted Items from Server” button
A window will pop up listing all messages that have been deleted and are queued for permanent deletion after 30 days. You can restore individual message from this list.
Web version of Outlook
Select the Deleted Items folder
At the top of the messages list, you will see a link to “Recover items deleted from this folder” that will take you to a list of messages that can still be recovered