As someone with deep experience in MIME encoding/parts, HTML for emails, and email client support for different HTML/CSS/image content, this is a sinkhole.

The world will be better off when we fork HTML so there is one standard email-safe version that all modern email clients support natively. There’s entirely too much security surface area to put arbitrary HTML into emails and expect any 2 email clients to render it correctly / the same.

Email needs its “no more IE6” moment.

> There’s entirely too much security surface area to put arbitrary HTML into emails ...

We manage it with browsers though.

Don't get me wrong, I've never liked html in emails to begin with. It's the same issue that markdown and every other rich text system has regarding where to draw the line. HN even strips most emojis (and I think that's a good thing).