So the idea here is if someone emails you who doesn’t know you they get an email back to say they can only send it to you if they pay, unless they know you personally, in which case they can request that you just approve the email. If they want to send you an email unsolicited they have to pay.
I turned it on and tested it for an hour or so but unfortunately it bounced some emails from Amazon !!!! Which I kinda wanted. So they could improve it by having their own whitelist with mail addresses like amazon.co.uk/.com.