Email is an open protocol. If I send an email that's illegal, say death threats or child porn, the government can put me in jail. There doesn't need to be a single controlling entity for that to work.

The process of doing that involves investigation, subpoenas, and warrants, and is subject to laws created in a more or less democratic process. No part of it requires anyone to prevent me from sending illegal emails, just an apparatus to punish me if I do.