So what if we just change email to work like this: Mail server will not let incoming messages through unless you've first A) sent a message to that domain AND B) received a reply that doesn't look like an error or bounce.
Yes, you'll have to send an email somewhere with little to no content to initiate reception of things like invoices, password resets, and monitoring emails. Is that such a bad thing?
Yes, spammers will desperately try to get you to send an email, any email, to their domain, or cybersquat on common typos. These problems might have easier and better solutions than letting tech giants takeover a formerly open Internet protocol that anyone should have the ability to use.