Here is what I use.

  # convert markdown to html via pandoc
  # https://unix.stackexchange.com/questions/108485/send-    email-written-in-markdown-using-mutt
  macro compose \e5 "F pandoc -s -f markdown -t html \ny^T^Utext/html; charset='utf-8'\n"

Yes please! This sounds intriguing. I send plain text only from mutt but including HTML from Markdown via Pandoc would be very cool.