One choice quote on email encryption systems:
OpenPGP is hard to use, and S/MIME can only be maintained by IT departments. These tools were never popular, will never be popular, and don’t even encrypt most of the metadata leaked by email.
And another quote, this time on how email is fundamentally flawed:
The lesson of EFail is that you can build everything well, but if you’ve built on a bad foundation, there’s no structure strong enough to stand.
It’s a great piece for techies to share with non-tech colleagues that want to understand a bit more about why email is the most dangerous attack vector for most users today.