If you are unable to enable the reading pane in Outlook because all the options are greyed out (as per image below) it may because you have your display/s in portrait mode.
Follow the stpes below to re-enable the Reading pane options
- Open Outlook
- Click on the View tab
- Click the Layout button and select Reading Pane -> Options
- Uncheck “Turn on automatic full-screen reading in portrait orientation“
- Click Ok
- You will now be able to turn on the reading pane