I don't see how you avoid some company reading your email and still have automatically indexed, infinitely scalable email in-boxes. Gmail is still the best game in town for this reason. The AI features are getting increasingly good--Gmail automatically creates calendar entries based on email content which is a pretty nice feature.

More generally most cloud services are going to have the same properties. It would be more useful to define clear bounds of what companies can do with your data and back them up with workable legal protections.