Many (most?) emails can be read in plain-text format even if they were written in HTML. The email often comes encoded with an "alternative" plain text version; of course you need a client that will show you that version instead. In my experience most personal email (i.e. not automated/form mails) I receive has a plain text alternative version that works fine.

For emails sent by an evil client that doesn't provide a plain text version, you can consider a tool that attempts to convert HTML to plain text (though I don't have a suggestion for this yet). Fall back on reading the HTML version only if the above fail.

- experience from working on / using my own mutt-like terminal email client.

> For emails sent by an evil client that doesn't provide a plain text version, you can consider a tool that attempts to convert HTML to plain text (though I don't have a suggestion for this yet).

I use emacs to read my email, and w3m to render HTML email as text. It does a good job. Newer emacs includes its own web browser (eww) but I have not tried it for HTML email rendering since I'm happy with w3m.

Replies always go out in plain text (my preference) but if you want to send HTML there are ways to e.g. write your email in org-mode markup and have it converted to HTML when you send. But IMO if you want to send "rich" email then just use a client that does that natively.

Mutt + Lynx does it well, too

Similar to the other child comment: elinks can format HTML as plaintext.

I have this as my .mailcap and it Just Works (TM) with mutt:

  text/html;  elinks -dump %s; nametemplate=%s.html;          copiousoutput

You can also use pandoc, I had better results with this:

> text/html; iconv -f %{charset} -t UTF-8 | pandoc -f html -t plain --wrap=preserve; copiousoutput; nametemplate=%s.html; description="HTML eMail";