When you delete an email from your mailing account using Outlook and IMAP, it still displays the message but puts a line through it. These messages live on the server until they are "purged," taking up space and are viewable in other clients (such as webmail).

To permanently remove your deleted email from within Outlook, choose Edit | Purge Deleted Messages.

To add the Purge Deleted Messages button to your Outlook toolbar:

1. Choose View | Toolbars > Customize…
2. Choose the Commands tab and click on the Edit Category.
3. Scroll down the commands list and select Purge Deleted Messages.
4. Click and drag the Purge Deleted Messages button to the toolbar at the top of the screen and drop it next to the Delete button.