By default, the great Mail User Agent MU4E prefers Plain Text mails over HTML. This configuration can be overridden via mu4e-view-prefer-html, but there's probably few of us who would do that.

However, you might still see a whole lot of HTML emails. And when you check if they have a plain text version, they might have one! There's a reason for that. MU4E has a 'HTML over plain text' heuristic with this official rationale:

Ratio between the length of the html and the plain text part below which mu4e will consider the plain text part to be 'This messages requires html' text bodies. You can neutralize it (always show the text version) by using `most-positive-fixnum'.

This heuristic overwrites the default setting (and configuration) that Plain text should be preferred over HTML!

In my experience, HTML Emails are WAY longer than only 5x the Plain text (Doodle, Airbnb, Meetup, etc), so this will yield me a lot of false positives whereas I have never seen a "This message requires HTML" body. Since I realized that MU4E has this heuristic, I overrode it just like the doc string told me to and am an even happier MU4E user.

(setq mu4e-view-html-plaintext-ratio-heuristic most-positive-fixnum)

NB, if you want to be able to read HTML emails, that's totally and 100% supported within MU4E! You can render them as:

• Text within a regular Emacs buffer
• PDF within a regular Emacs buffer - complete with styles and all
• Open the email in a browser through a shortcut

For these and other goodies in MU4E, please have a look at my configuration: https://github.com/munen/emacs.d/#mu4e