> Talking to non-tech people means you're going to be copy-pasting screenshots and replying in blue text next to their bullet points that was written in black text.

None of that requires HTML. Using ">" to denote previous conversation quotes is the standard and they normally get highlighted different than reply text. And images just need a decent 'drag-to-add-attachment' flow.

Marketing emails don't matter as they are an abuse of the platform.

The entire reason email (and the internet) took off is because there are many ways to use it, for many purposes.

Handing down diktats about the correct use cases and workflows for a flexible thing that is currently being used by billions of people in billions of ways - like email - will either reduce your personal relevance to them, or, if you succeed in pushing your vision onto the popular thing, drive people away from it.

> legitimate marketing emails

I don't think there is such a thing.

I receive many such emails that I signed up for and am happy to get.

The senders of those emails are happy to send them.

Unless you - an unrelated third party - think you have the right to insert yourself into this business relationship, it's completely legitimate.