PGP users,
I implemented a simple #efail exploit for Apple Mail, which is vulnerable to direct exfiltration with its default settings. The mitigation, disabling remote content, works but is brittle. So never click "Load Remote Content". (Thunderbird/Enigmail is vulnerable in a similar way, but I haven't tried that one yet.)
https://www.youtube.com/watch?v=_67Pz9zpPb0&feature=youtu.be