@liaizon
One word:
G-mail.
E-mail too is federated, decentralized and open-source. Doesn't stop Google from spying on, like, a half of E-mail users. And that's more than enough for most uses. Why is that? That's because a lot of clients made G-mail the default. Even Elementary Mail, which I love, shows this (1) when you start it the first time. And when you want to use some other server, it suddenly blows up to this (2). It becomes a chore to set up, and considering E-mail, being what it is for that long, already has all kinds of autodiscovery tools like MX or SRV records or plain damn Thunderbird ISP Database, and failing all that, just poll the goddamn standard E-mail ports on the domain for auth methods, I'm prepared to wait 500 miliseconds while you do it, it's not hard.
So. Do we really need another Gmail?