The email protocol isn't complicated though. Back before spam was a thing, lots of people could just open a port and manually talk SMTP (you could send messages as Santa, or whatever). The only service Gmail provides that's not trivial (and I mean, something that can be done in a whiteboard interview) is the spam protection.
A more advanced classifier certainly do better these days.
However, it's also a closed system and you need to get crypto from somewhere. A centralized exchange is the most efficient facilitator of buying/selling crypto, and after that you can withdraw it and enjoy digital transfers without a centralized party.
(You can also get crypto buy mining or selling things for it, or even buy it for cash, but an exchange like Coinbase is much faster and more convenient.)
That’s where the biggest money and the highest yield is achievable anyway. And the quality of decenttalized offerings is rapidly improving.