Follow these steps to automatically empty your “Deleted Items” when you Exit your mail program.
Click the File tab and then Options. Select Advanced. Under Outlook Start and Exit, select the Empty the Deleted Items folder upon exiting check box.
To be warned before automatically deleting items, click on the Advanced tab, under Other, select the Prompt for confirmation before permanently deleting items check box.
Select Tools>Options from the Command Menu. In the Options dialog box select the Other tab and then select the checkbox at the top, Empty the Deleted Items folder upon exiting. Select OK to save the setting.
Click on the Tools menu and select Run Schedule. Click on Edit Schedules. Double-click on Empty Deleted Items Folder and change Manually to On Quit under the When section.
In the top right click Options/See All Options from the menu. Click Settings in the list on the left. Click Mail (from the four icons at the top). Under Message Options, select the checkbox next to Empty the Deleted Items folder when I sign out. Click Save (at the bottom right of the web page).