While Outlook Express is no longer included in Window 7, We have several small clients and home users running Windows XP that use this program. Last week we encountered 2 different users that could no longer delete items. The problem was that their Deleted items folder had gotten to 2GB, and 2GB is the maximum size allowed for any of the folders in Outlook Express.
Even after emptying the Deleted items and compressing the box, th user could still not delete items.
The solution is to close outlook, and find the deleted.dbx folder (Documents and settings/username/Local settings/application data/identities/abcdefgh1234/ where Username is the user logged into the computer, and the abcdefgh1234 represent an identity on the machine) and delete the file deleted.dbx. When outlook restarts, it will create a new file and users can continue to delete items