How to permanently delete an email message

Outlook for Windows:

1. Hold the Shift key while clicking on delete on the message you wish to permanently delete.  You’ll be asked to confirm permanently deleting the message.
2. Go to Folder tab at top of Outlook.  Select Recover Deleted Items.  Select the message & Purge selected items.  
3. The message is retained for 30 days (i.e. the Deleted Items Retention Period configured on your mailbox)
4. After the Deleted Items Retention Period expires, the message is marked for permanent deletion and will be purged from Office 365 in 7 days. This is controlled by Microsoft.
5. The message is now entirely unrecoverable.

Outlook for Mac: (See Office portal instructions)

Office portal user (http://office365.acadiau.ca)

1. In your inbox, select the message you want to delete.
2. Above the reading pane, select Delete. (Your message is now deleted)
3. Under Folders, select "Deleted Items",select the message you want to delete again.
4. Above the reading pane, select Delete again.
5. Warning: "Do you want to permanently deleted the selected items?"...select OK (Your message is now only recoverable)
6. At the bottom of the deleted items message list, select "Recover deleted items" button.
7. Select only the message you wish to permanently delete and make unrecoverable.
8. Select the delete button a final time.
9. Warning: Are you sure you want to delete the selected item? You won't be able to recover them.
10. The message is retained for 30 days (i.e. the Deleted Items Retention Period configured on your mailbox)
11. After the Deleted Items Retention Period expires, the message is marked for permanent deletion and will be purged from Office 365 in 7 days. This is controlled by Microsoft.
12. The message is now entirely unrecoverable.