Well, I take that back. Sometimes I will use Tutanota in a disposable VM. But tutanota keys only exist client-side. Tutanota is a different model tho. It is not interoperable with PGP. If you want end-to-end encryption, both users must be using Tutanota, or you will have to share an assymetric key (password) out of band with a non-Tutanota user.