Other colleagues email starting giving them previews of unread items following some changes to our system by our IT people. Not everyone was affected but it was really annoying to those affected by this. It took me ages to find this
solution and it's a lot simpler than many suggested answers I found. I hope this helps -
To change this setting to 'no preview', in Outlook go to the following:
View (tab)
View Settings (to the top left)
Other Settings
Auto Preview - select
'No AutoPreview' and then OK, OK