Does anyone know of an email service, add-on or tutorial that allows for mimicing the one feature that intrigues me about HEY e-mail: opt-in for receiving emails from someone.

i.e. the default would be that someone who is not yet an approved sender ends up in a separate inbox where I have to confirm if I want to keep receiving email from them or not. I think HEY calls this ’the screener’.

Or if you’ve tried this fature and don’t like it, that would be cool to hear about as well.