[Fice]

Federation does not solve the problem. Eventually most users will flock towards single most popular instance of a federated service. Email is federated, but most users betray it by choosing the most popular provider (Gmail). And Google will happily drop email federation "to protect users from spam" when they get enough user share as they did with XMPP.

[erez]

Technically email isn't federated. Like the web you have an email server that hosts an email address and all mail to and from go to it, and while you can IMAP to it through a client, and host a "mirror" of it, to send/recieve emails you still need to go through the single email server.