Markdown is great. I use it all day, every day. But, email clients are mostly targeted toward general users. General users don't know what Markdown is, don't kn

Markdown is great. I use it all day, every day. But, email clients are mostly targeted toward general users. General users don't know what Markdown is, don't know how to use it, and don't want to use it. General users want WYSIWYG. There's nothing wrong with HTML. It is the predominant standard and along with CSS, very expressive.