Food for thought:
Most people use big corporate servers for email, like Google. So if you
communicate with these people, which you probably do, then these
corporations, and likely your local government by proxy, can find out who you
communicate with and when.
However, if you and someone else both self-host your email, then any
communication with that person will not be known by some corporation, and by
proxy your local government, except to the extent that your ISP can monitor
it (which I'm not sure about, but I assume it probably can't if the servers
encrypt their communications with other servers). So self-hosting, or using
the server of a friend, doesn't completely solve the problem, but it's
definitely worthwhile: it at least makes the picture about you incomplete.
Note that the same applies to any federated thing (e.g. Diaspora, GNU Social,
pump.io, Friendica).
