If you are running Microsoft Office Version 2011 - Build 13416.10000 or higher, that introduced a feature that automatically offers you short suggested responses while replying to an email in Microsoft Outlook client. This makes it easier while replying to an email that needs just a few words.
Though it was a useful feature, not all users want to see these suggested replies. So, with the latest Microsoft Office Version 2108 Build 14301.20004, the company added an option to turn the feature off.