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I think this is, aside from the security concerns, why many chat applications, forums and tools like Github/Gitlab have switched to standards like Markdown for text formatting. I can see the value in linking, embedding images, highlighting through bold and italic text, and underlining. Even code can be useful inside an email. Markdown or a similar language would serve most people very well, much better than HTML. Non…
If emails were written and parsed as markdown, I might (!) change my opinion about it. But HTML is vastly too feature-rich to be sane. I think showing images inline (such as in Github-flavored Markdown) is still too feature-rich. But lists, tables, monospaced blocks, italic, bold ... these are fine. Embedded images aren't conducive to being parsed by a script.
My perfect world email markdown will probably be different from yours. For productivity, anything more than slightly stylised text is just unnecessary, but in practice, most email isn't used for productivity anymore. Instant messaging has replaced email as a means of conversation in all workspaces I know.