NSA can't decrypt Proton-to-Proton, Tuta-to-tuta, etc Emails?

[master.on]

If you send messages within the same encrypted mail provider
NSA can't decrypt them?
So they have to ask for a judge order to get the Email to provide the decrypted Emails?

 

[CdnGuy]

At Protonmail, Lavabit and Tutanota, Even the Founders Can’t Read User Messages | Observer
Protect Your Email From the Cops So Congress Won’t Have To