Compiles annotated text mail into html using the Markdown standard

 muttdown is a sendmail-replacement designed for use with the mutt email
 client which will transparently compile annotated text/plain mail into
 text/html using the Markdown standard.
 It will recursively walk the MIME tree and compile any text/plain or
 text/markdown part which begins with the sigil "!m" into Markdown,
 which it will insert alongside the original in a
 multipart/alternative container.
 .
 It's also smart enough not to break multipart/signed