Hmm. I haven't tried protonmail, but I see that with other emails that I receive. And what are the purpose of cryptocurrency payments? Is it for receiving and sending to another proton mail? I will research more about it when I get home.
Protonmail is not a service like Gmail.
They are based in Switzerland (all user data is protected by Swiss legislation).
They do not ever read your emails (Google reads all of them)
End to end encryption, open source...
However, the free protonmail version is limited to 500mb. If you need more, you need to pay. It's high quality service, so it can't be free like Google (where you are the product).