1. Click File.

2.  Click Options.

3. Click Mail.

4. In the 'Outlook panes' section click Reading Pane. This will show its options. It's currently set to "Mark item as read when selection changes".

5. Click the box next to "Mark items as read when viewed in the Reading Pane." You can also change the delay timer associated with this option to as low as 0 seconds. Single key reading lets you move from message to message by pressing on the space bar. The full-screen reading in portrait orientation option toggles how Word Documents are preview in Outlook.

6. Click OK.

Now messages will be marked as read at the speed of your preference.