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

Instructions
- 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

Thank you so much. It has been bugging for ages, never contemplated that portrait mode on my monitor would cause the issue
The reading pane only displays the header for the email
I cannot find a layout button, sorry! please help on this ASAP!
Make sure the Outlook window is maximized. If there is no layout button there will be a Reading Pane button above the word “Layout”