Open Outlook and click the “File” tab.

On the backstage screen, click “Options” in the list of items on the left.

On the Options dialog box, click on “Mail” in the list of items on the left.

In the Outlook panes section, click the “Reading Pane” button.

Check the “Mark items as read when viewed in the Reading Pane” box to make Outlook mark your messages as read when you view them in the Reading Pane. By default, Outlook will only mark a message read after you’ve been reading it for 5 seconds, though you can change this. We entered 0 (zero) in the “Wait X seconds before marking item as read” box so our messages would be marked as read as soon as we select them.

Note that the “Mark item as read when selection changes” box is automatically unchecked when you check the “Mark items as read when viewed in the Reading Pane” box. Only one of those two check boxes can be selected at once. Click “OK” to accept your changes and close the dialog box.

Click “OK” on the Options dialog box. Now your messages will be marked as read as soon as you select them in the reading pane, or soon after, depending on how many seconds you told Outlook to wait before marking the item as read.