Note: This Article was written for Outlook 2003, but should still work (with modifications) for other versions.
Are you running your Outlook email through IMAP and getting a strikethrough in your messages when you hit Delete? Well, to completely remove them, your will need to "purge" your deleted emails.
There are two ways to do this:
Select Edit and then hit Purge Deleted Messages, which will purge your messages. If this is tedious, look at version two.
Let's add the Purge Deleted Messages button to your Outlook toolbar.
Step 1: Choose View then Toolbars > Customize
Step 2: Select the Commands tab, and click on the Edit category
Step 3: Scroll down the Commands list and select Purge Deleted Messages
Step 4: Click and drag the Purge Deleted Messages to your Outlook toolbar
Step 5: You're done. Now you just have to click on this new button to purge your messages.