Render HTML email when there's no text/plain alternative
If there's no text/plain version of an email component, mutt defaults to just rendering the html, regardless of the mailcap file.
To make it do something more useful:
text/html; lynx -force_html -dump %s ; copiousoutput
One downside of this, is that lynx no longer can run interactively (you can't follow links from a html email). Instead lynx will print out a references section at the bottom with all the embedded links.