Office 365 (Outlook 2013 / 2016 / 2019 for Win) - Turn On or Off the Message Preview Option
1. Select the View tab from the ribbon and click on Message Preview.
You have the option of previewing the first line/s of the message content in your inbox list and other mail folders, OR you can turn this option off.
2. It will bring up a window that has the following selections:
3. If you don't want the first line/s of message text to appear in your inbox (or other mail folder) view, select Off.
4. It will bring up a window that says, "Change preview setting in All Mailboxes or This Folder". Select your preference and your change will take effect.