I have found that running the html email through w3m generates usable text in almost all cases: text/html; w3m -I %{charset} -T text/html; copiousoutput

I have found that running the html email through w3m generates usable text in almost all cases: text/html; w3m -I %{charset} -T text/html; copiousoutput; ... in your .mailcap. The result is usually better than what ends up in in the text portion of dual text/html emails. Particularly nice when someone thinks they need html to show a table.