How to Turn OFF the Reading Pane for OWA in Office 365
To turn off the reading pane in office 365 for OWA, follow the following steps.
1. When logged onto OWA click Options and select Display Settings as shown in the Figure below.
2. In the Display Settings window select ‘Hide Reading Pane’ under Layout. Also tick the checkbox next to ‘Apply to All Folders’ and then click OK.