You need to turn off the preview page. With that open, any message that appears will be considered read. Also, it is quite dangerous to have that reading pane open. Reason being that if an email has something in it that may harm your computer, you have opened it with the preview pane. That is why they say never open an email from someone that you do not know. Go up to View –> Reading Pane, Off. This should take care of your problem.