Could someone explain to me the lore that email can't be make secure? It seems to me that all the steps described on this article could be automated behind the scenes by a good local email client.
* Email reveals large amounts of metadata, including message content (which is what a Subject: line is), which is a characteristic shared by no secure messaging system. The graph of who talks to who and when is immensely important, and the best secure messengers (Signal, in particular) go through trouble to obscure it.
* Modern secure messengers are forward-secure, so that a compromised key doesn't allow attackers to retroactively decrypt old messages. Since messaging traffic between selected peers is almost always low-volume, any reasonable threat model assumes every piece of ciphertext exchanged between peers has been archived by adversaries. With PGP, a key compromise at any point in time reveals the contents of every one of those messages. The best secure messaging systems are not only forward secure but also have a notion of "future secrecy" allowing them to recover from ephemeral key loss.
* Email clients are inhospitable to cryptography; in particular, many of key features of clients (like search) rely on having a local archive of plaintext. The UX in email clients begs users for catastrophic failure, like accidentally top-posting a reply to an encrypted messages with an unencrypted message.
All four of these problems are, in isolation, total dealbreakers for serious secure messaging.
SMTP email is janky and outmoded and it's a little amazing that we all use it as much as we do; it's long overdue for a replacement. If you need to communicate securely with someone else, you should do so with a secure messenger like Signal, not with PGP and email.
I'm no expert in security, but my intuition is that the likelihood that my signed ubuntu plus gpg leak secrets is significantly lower than my who-knows-what-the-hell-its-doing android with signal, right? You gotta agree with this at least.
Snowden in particular did much dumber things than using PGP: he used Lavabit, a "secure email provider" with an architecture any expert could have told you from 10 miles away to avoid, and some amount of the Snowden/Poitras/Greenwald coordination occurred over CryptoCat, which was grievously broken in several different ways --- it is almost certain that every message exchanged between those parties on CryptoCat has been recovered by SIGINT agencies.
People wonder why crypto engineers on message boards are so shrill about this stuff. This is why.
Experts I know recommend iOS above any other consumer platform (though that might have something to do with Apple's hardware and of course you can't use iOS without Apple hardware).
When talking with the security folks I know, this is not a rare opinion. You can't trust the source of any comms platform. So you have to reverse engineer the binaries. Once you get into that game the more important things than open source are, do you trust the team? Is the protocol open and vetted? Does it rely on 'odd' implementation details.
The idea that the nature of the software license of the OS that your comms platform is running on, is important for its security characteristics, does not seem to be something that the experts I know believe. Quite the opposite. It seems to be a signal of people who don't do this sort of research for a living.
If anyone wants to tear out excess hair, watch Citizenfour's scenes with Snowden and the rest on their computers. The main argument against the omniscience of the intelligence agencies is that they didn't walk into that hotel room on the first day.
Besides technical issues, watching Snowden try to get Poitras and especially Greenwald to adopt security based on operational discipline and CLI *nix tools is both hair-raising (easier to tear out that way) and laughable. Clearly he never had to work with end users. IIRC, in his initial instructions to Poitras he tells her 'if you have trouble setting up that encrypted connection, just ssh to the ip address and use the tool of your choice.' (If you don't understand why that is laughable, you haven't worked with end-users either.) Greenwald seems completely at a loss - 'I made my password (to the data on which Snowden's life and the whole news story depends) simple because I have to use it all the time - is that ok?' Sure, why not at this point?
Signal started out with SMS, which was quickly abandoned. Your target would basically get a SMS message saying something like "someone is sending you an encrypted message, please install signal to read it".
Seems like a imap proxy could do similar. Use a DHT to track who has a public key. Send anyone who doesn't a "please install this plugin/proxy/whatever to read this message". Have a signal like autogeneration of keys tied to an email address instead of signal's phone number.
Could even have a service like <username>@whisper.com to allow people to use their favorite email client (like thunderbird) to send/receive email and leak less metadata. The imap proxy would use a signal like transport for anything matching @whisper.com.
I seem to recall a project like this mentioned, even a thunderbird plugin or some such.
Not as secure as signal, but better than today's default.
No choice in clients, requiring a cell number, no search, and no threads.
Hard to imagine someone that uses email heavily with large volume of email trying to cram that much information into signal and then be able to find it again years later.