That’s cool but I like to have a central client for all my email providers. I’ve decided to go to fastmail which is good enough for my threat model. The thing that really convinced me is their blog post.
The main thing I care about is the security of the text in transit, and the philosophy of the service I’m using. All respectable mail providers use TLS (even gmail and outlook) but I don’t like their advertiser dependent business model. Proton, tutanota, and I think startmail do respect privacy, but I believe it’s dumb to depend on an external server if you’re that paranoid about your communications that you need to have your email using PGP. Just encrypt your own stuff and tell the other party to do the same. Or self host everything.