Items that you delete are moved to the Trash folder, but these files aren’t permanently deleted until that folder is emptied. Over time, the contents of the Trash folder can consume a large amount of your data file or email server storage.
You can only manually empty the folder.
Manually empty the Trash folder
1. In the Mail pane, right-click the Trash folder you want to empty, and then click Empty Folder.
Note: In Outlook for Windows the Trash folder is called Delete Items folder. For more information,