Outlook.com - Prevent the recovery of deleted messages
When you delete messages under Outlook.com, they are sent to the "Delete Folder". You may think that upon clearing the Delete Folder, its content will be cleared too. But this is not the case. Outlook provides a link allowing you to restore deleted messages.
To disable the recovery of deleted messages:
Sign-in to your Outlook.com account.
Click on Settings > Options.
Go to "Customizing Outlook.com" > "Advanced privacy settings".
For the "Deleted messages" option, select "Don't let me recover deleted messages--once they leave the Deleted folder, don't give me a link to get them back".