I think the main issue at play here is quoting. In particular, how bad rich text/html mail programs are at dealing with inline quoting. In my opinion, that’s th

I think the main issue at play here is quoting. In particular, how bad rich text/html mail programs are at dealing with inline quoting. In my opinion, that’s the main “feature” of email communication that has been lost over the years. On the top replies make it difficult to follow a nested thread of emails. If html email clients handled this better, I don’t think there would be as much of a problem. I think you’re right though that plain text acts as a bit of a shibboleth to differentiate “advanced” users vs luddites. But the main thing that I’ve heard people complain about with respect to html email is the loss of inline quoting. Plaintext has its issues too— in particular long line soft wrapping. Which some would argue would be better supported if html email hadn’t become so popular.