Why have HTML email in the first place? No other messaging client lets you send entire HTML documents as messages. Just send me some words and a link to click on in a proper browser. The fact that HTML email is so bloated and a nightmare to eyeballs eveywhere is (IMO) a huge reason why conversations (even professional ones) shifted over to Slack, SMS, WhatsApp, FB Messenger, etc. I want a place to talk to people, not to shitty template engines. But if you're going to automate my conversation, use words, not posters.

You're comment made me think about why we actually use slack/IM when email is just as capable and I think the answer is that I can have notifications turned on for IM and I can't do that for email. Which means I respond much slower to email.

IM is one of the last places on the internet not filled with automated crap, advertisers and spam. And to be fair, some of that automated crap I actually want and browse through at a later time but IM explicitly separates real time messages and newsletters.

Email supports instant notifications, via your provider’s app or IMAP IDLE. I use Fastmail and get push notifications for email the instant it is received.

The point is if I turned on instant notifications I would go insane because they would never stop. I receive lots of emails and a lot of them are not very important or at least not urgent. While every IM I receive is something I at least want to glance at now.

That point, frankly, applies to some Slack workspaces too. Some of them just have too many notifications to keep track of.

Email notifications are flexible. I can choose to receive notifications only from contacts, search terms, or specific people.

I'm intrigued by that idea. Markdown or Markdown-like subsets have proven to be sufficient for communication in a variety of media (Slack, Wikipedia, forum comments, GitHub issues/comments, etc.)

Email clients are a bit of an oligopoly, so execution would depend on which player(s) are involved. Most of these initiatives would need an "everyone but Outlook" coalition to succeed.

A few thoughts on implementation:

- Multipart MIME is still a big part of HTML mail, so it would make sense to piggypack on that support. Instead of adding a new MIME attachment for Markdown, it would make sense to extend the existing support for text/plain renditions and find some way to signal that it's Markdown. (e.g. text/plain; charset=UTF-8; variant=MarkdownMail)

- For mail clients that aren't Markdown-aware, it would be important to produce an HTML-rendered variant with a reasonable style sheet.

- A Markdown-first mail client would either need to limit formatting to Markdown or soft-block access to non-Markdown formatting. ("Custom text colors will not be visible on some devices and may be lost when replying. Continue?")

- When viewing a Markdown-enabled message, a Markdown-first mail client would render the text/plain variant in its preferred style sheet, not the HTML-rendered variant.

- When replying to a Markdown-enabled message, a Markdown-first mail client would use the text/plain variant as the source of truth for quoted replies, not the HTML-rendered variant.

A few tricky areas:

- Mail clients would need to agree on a Markdown dialect, especially for extensions like tables.

- Markdown isn't very incompatible with quoting. There would need to be a solution for inline quoting.

- For everyone's sanity, it would seem important to agree on a delimiter to separate prior messages and their headers.

- To not be worse than HTML mail, we'd really need a way to signal that a paragraph is part of a mail signature so that it can be rendered in a subtle way. As much as we might wish that mail signatures would just go away, they will continue to be used, and rendering them as standard paragraph text just makes them more distracting.

Not a bad idea.