Like many "technical solutions", at least most of the answer is easily found - PGP.
Also, like many "technical solutions", the answer _isn't_ a technical solution. The bigger problem is people. PGP _will_ secure my email. But out of my almost 1000 contacts I've got only a few dozen with PGP keys.
While 95%+ of an email network's users _aren't_ using encryption, the network is fundamentally insecure. That's not an engineering problem - that's a people problem. The EFF, Wikileaks, CryptoParties, and individuals like you and me – have a far more important role in making sure "a sustainable, fully encrypted email service untouchable by the Feds" exists – not by building anything new, but by convincing your friends and coworkers and bosses and parents that it's important and possible right _now_.
It's not a people problem, it's a design problem. The technology is there, it just needs to be integrated in a way that makes it 'just work' for everyone.
I'm not so sure - "strong passwords" mostly "just work", but ~25% of passwords in published hash dumps still fall to the RockYou wordlist, and another 10 or 15% with the best64 rules in hashcat.
When given the option between "laziness" and "security", it's abundantly clear which most people choose.
I strongly believe that as well as "easy to use technology", we very much need to educate our friends/family/coworkers on the need for encryption and the risks of not using it.
Also, like many "technical solutions", the answer _isn't_ a technical solution. The bigger problem is people. PGP _will_ secure my email. But out of my almost 1000 contacts I've got only a few dozen with PGP keys.
While 95%+ of an email network's users _aren't_ using encryption, the network is fundamentally insecure. That's not an engineering problem - that's a people problem. The EFF, Wikileaks, CryptoParties, and individuals like you and me – have a far more important role in making sure "a sustainable, fully encrypted email service untouchable by the Feds" exists – not by building anything new, but by convincing your friends and coworkers and bosses and parents that it's important and possible right _now_.