What happened to the idea of using cryptocurrencies to prevent email spam? Here is a crazy idea - those with too much inbound traffic should have an email client that:

I ) Shows five emails per day, the rest are blocked by the client.
II) Senders bid to be one of those five emails. Last seven-day average price is publicly available for bidding guidance. If the email isn't delivered the sender gets the money back.
III) Proceeds are donated to charity or sent wherever the reader wants if the reader doesn't like the idea of making money from reading emails.

Such is the beauty of economics that now everyone can stop keeping their email a secret and instead auction off their attention and those previously unreachable become reachable.