By default, Outlook 2010 marks emails as “read” when you click on the emails subject title. To change this behaviour so that the email only displays as “read” if you actually open the email, or forward, follow these steps:
Step 1 – Click on FILE in the top left of Outlook 2010, then navigate to OPTIONS on the left hand side menu.
Step 2 – Select the MAIL menu on the left, then click the READING PANE button on the right.
Step 3 – On the new popup – UNTICK the option for “Mark item as read when selection changes“. Then click OK. The setting has now been applied.