A key part of OP's advice was to get email at your own domain. Then you can switch email providers if it comes to light that the provider you're using is doing

A key part of OP's advice was to get email at your own domain. Then you can switch email providers if it comes to light that the provider you're using is doing creepy shit with your email. And speaking of Fastmail: I sincerely doubt they're reading your emails. They make money solely by providing email services to (for the most part) businesses. If it came out that they were reading emails A) it would probably be a violation of their contractual obligation to their customers, and B) their reputation would be permanently destroyed.