There is a function in Outlook that means you may risk missing e-mail messages: all you have to do is mark an incoming e-mail and browse to the next one, and the “unread” marking disappears. You can disable this function if you wish.
This is what you do:
1. Click the View tab.
2. Click Reading Pane and then Options.
3. Deselect Mark items as read when selection changes.
You must now open a message for the bold marking designating it as unread to disappear.