How would you "end to end encrypt" an email going from Super Secure Provider A to Outlook or Gmail? The encryption stops the millisecond it leaves Provider A's servers.
Nothing about that is "email" anymore. The same method can be used to make "password protected SMS" for example. Just send a link to a website and a password. Encryption!
What we need is actual public key encryption/signing support on mail services, but that's not going to happen ever.