There are two automatic policies in effect for email retention.
The first policy concerns junk email. Every night the special folder labeled “Junk E-Mail” has items older than 7 days removed.
The second policy concerns the “Deleted Items” folder. Every night items older than 21 days are removed from this folder. These items can still be recovered using the “Recover Deleted Items” option for another 21 days. We recommended that you disable the feature to automatically empty your deleted items folder from Outlook and owa.win.udel.edu.
If you've deleted a message accidentally, you can recover it using the following steps: