Interesting list. This got me wondering if there are any zero-knowledge email providers out there, especially ones that let you use your own domain. Only thing I found so far though is an empty Quora question:
For that particular need, I'd expect that I'm rolling my own, or using a service provided by my business or something. At the very least, I'd assume that I'm paying for it, and even then, when you get to that level, you probably want to just do it yourself for the knowledge that you really do have complete control.
Yup, I'd expect to pay for such a thing, no problem with that, just don't see any even for pay. Rolling my own is the other alternative, will probably end up doing that.