Pretty sure somebody has already posted this here, but it's worth re-posting over and over again!
https://useplaintext.email/

Thanks to #SourceHut for putting this together!

@rysiek The RTL objection is a good one:
https://news.ycombinator.com/item?id=20514414

Similarly, virtually any non-Roman characterset.

That said, yes, I'm a fan of ASCII / plain-text email where that is even remotely possible.