I tried to register an alt account using my Proton Mail email address and it was not allowed. The error message is not helpful but I dug into it in my browser... Looking at response body of the XHR request posted by the sign-up form `@proton.me` is apparently classed as "low trust" and my address is flagged as a disposable email address (it's not, I've had it for a while). My main account uses a Yahoo email address. I am not able to register another account with Yahoo because each one