I'm sure those who have run and maintained a mail server, and cryptologists, would probably want to throw something at me for spouting crap, but please bear with me.

Firstly, the Fediverse appealed to me because I knew it was the true answer to these centralised social media platforms. But the problem is that cross server encryption is difficult. For example, I hear that Mastodon servers cannot federate with each other properly if end-to-end encryption was rigorously implemented.

Secondly, there are EU laws that are proposing that messenger services should be interoperable. So in theory, Signal users can chat with WhatsApp user and Telegram users. They say it is possible with open protocols and API tooling.

So together, I wanted to know if this was possible for email. I know that some of the ancient protocols (in computing timelines) don't lend themselves very well for the hostile encryption heavy requirements of the modern internet, but I think it is possible to envision an grassroots alternative.

Am I completely missing something super critical? or are there already federated, end-to-end encrypted emailing services that can be easily spun up?