Odds are that you are using an IMAP email account in Outlook 2007.

When an email is deleted, a line is simply displayed through the email's subject line... and the email isn't 100% deleted until you manually "purge" it.

However, with just a simple change you can now delete emails as you expect to ... without having to manually "purge" each time.

Outlook 2007: Automatically purge the deleted items

You can configure Microsoft Office Outlook so that when you switch between folders, any items you have marked for deletion are purged from the IMAP mail server.

1. Click a folder in your IMAP e-mail account.
2. On the Edit menu, point to Purge Deleted Messages.
3. Click Purge Options.
   The Internet E-mail Settings dialog box opens.
4. On the General tab, under Purge Options, select the Purge items when switching folders while online check box.

Now, this doesn't immediately delete these emails, so there's one more procedure to do.

Outlook 2007: Hide deleted emails

To tell Outlook 2007 not to display the deleted emails:

1. On the View menu, point to Current View, and then
2. click Hide Messages Marked for Deletion.

If you are using the Reading Pane, you must turn it back on after using this command.
On the View menu, point to Reading Pane, and then click Right or Bottom.

Remember:
Be sure to do both procedures, otherwise you'll just hide the "deleted" emails... without actually deleting them !

Note: Instructions originally copied from:

• http://office.microsoft.com/en-au/outlook/HP100804201033.aspx