Most normies dont want to set up their own mail server, they just want to log into a "service" that allows them to send/recv mail. Thats how companies insert themselves into peoples lives, as a low friction and often free way to save time and effort (free but you're still the product). How are protocols going to solve that problem? Someone will still have to donate their time and effort to making other peoples lives easier and then you have centralization again. Unless a service is distributed by default I can't see any technical solution.