You don't need CA's for e-mail encryption. You need keyrings and networks of trust (I exchange keys with my closest associates via offline means; I sign a certificate stating that I vouch for the authenticity of their certificates; my associates can then choose whether or not to trust the signatures I've signed, and whether to trust the signatures they've signed again).
Yes, there's room for infiltration, but it is vastly better than relying on central CA's for this type of usage, because it allows people you trust to contradict infiltrators.
Of course there's no need to rely on a central CA - it's not hard to run your own, and you can make it reasonably secure - say, a small ARM Linux board with passphrase-protected private keys on a removable SD card. Generating the keys in a secure way is perhaps a bigger problem - untrusted hardware RNGs, poor quality entropy after boot etc.
One can also keep a virtual machine CA on a hardware-encrypted USB device (IronKey, say, depending on your level of trust with Imation) - it's easy enough to bootstrap a tiny Linux distribuution from source with just OpenSSL and some utility scripts to issue & revoke certs.
You don't necessarily need a $5000 HSM solution to issue your own SSL certificates at this level.
Well sure, I can issue them myself in a few minutes, the issue is that arbitrary mail servers won't be able to authenticate me. Which means we're means we're back to MITM attacks—better than plain text if the observer can't manipulate the data stream—but I wouldn't bet on it. Work with the assumption that the NSA is Mallory, not Eve.
I certainly wouldn't be comfortable with my peers having the opportunity to control my email and the myriad of accounts associated with it. I can't imagine they would be happy with me doing the same with their data.
> We also show how to configure encryption in their mail clients
Encryption is fairly useless without authentication, and we can safely assume that the NSA has control of Certificate Authorities.
> Think about it. There are enough tech geeks. Every geek should need to know how to do this anyhow. This will scale.
I've been battling with the concept of hosting my email for quite some time, and it always boils down to being a horrific thing to set up. There's a pile of easy ways you can screw up and make something insecure or spam-ridden. I spent a good day trying to put together a solution I was happy with, but couldn't.