http://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/blog/protonmail-secure-email-open-source
                                
                                
                                                                            Although our team of former CERN scientists, together with experts from MIT, managed to scale Proton Mail 1.x, a better solution was needed. With Proton Mail 2.0, we now have a new framework which we can easily scale to provide encrypted email to millions of users.