There are lots of drawbacks to an SMTP based service vs. something built on a newer protocol with client-side crypto everywhere, but email has a huge installed

There are lots of drawbacks to an SMTP based service vs. something built on a newer protocol with client-side crypto everywhere, but email has a huge installed base. This becomes a question of "good" vs. "perfect", but it might also be a question of "too dangerous to use" vs. "replacement" -- depends on threats, alternatives, and quality of implementation. I know one of the people at Proton Mail pretty well, and have met the others. Of all the companies doing secure email right now, they seem like the best.