Email me at my well known identity "whoever@whatever.com" -> my provider gives you a key that you must store and continue to use for the duration of our relationship. I can terminate it if I want. If you lose the key, you must ask for a new one. If you ask too many times, I can silence you forever. You'll have to provide your own identity when asking.

For noisy environments, I can choose to give you the key upfront and only allow for that style of relationship.

I could imagine encoding the concept of entity or organization type into the keys as well so that we can distinguish individuals from companies. Professionals, academics, official employees, etc.

If you delegate your key to another party, I can choose to pre-authorize it, manually approve it, or outright deny it. Extend it haphazardly or without my consent and you may be blocked.

I'd like that type of system.

Emails shouldn't have to change. The protocol should. Getting parties onboard might be hard unless a key stakeholder (eg. Google) decides to implement this, but they're in a position to unilaterally dictate.