I have a user on W10 pro using Office 2016 Pro Plus.
Question is specifically about Outlook.
When viewing mail in the framework everything appears fine, but when he goes to reply all HTML formatting in the message is lost and reduced to code. The setting in Outlook is showing HTML (as it should since original was sent in HTML), but messages are defaulting that way.
Same user has same Outlook mailbox profile on another machine with 2016 Pro Plus installed and no issues. Tried a bunch of setting tweaks found online, ran simple repair and online repair, tried different profile.