And what percentage of e-mails from people / human beings have those things?
Certainly marketing e-mails have fancy formats, but I've rarely seen any person at a companies I've worked at use any kind of formatting: generally most folks hit reply and start typing with whatever the default is. Hardly any italics or bold, and forget about fixed width (for things like CLI commands in technical discussions).
Heck, even Slack messages these styles are hardly used (on my current team I use them the most since I know that Markdown so it's easy for me to throw in some **, //, or `` in my typing flow, so I can highlight hostnames, CLI commands, etc).