This is why it's always struck me as unreasonable for proton to claim they care about user privacy. If they did, they wouldn't provide an email service, as it is inherently impossible to adaquately protect the metadata if it is sent to a different mail server. A better approach would be for them to explain why you can have email or privacy, but not both, and to point people to a separate service if they insist on email, so it is decoupled from any of their other services. Accepting payment through a means that isn't tied to your personal identity would be a good step too.