There's a company that implemented this for email using cryptocurrency. https://bitbounce.com/
Any unfamiliar senders get an autoreply asking for them to pay a fee to send the email. You as the receiver get paid this fee (-30%) for each email received (not read)
Interesting. Also, there used to be a feature for cell phones that was called "Caller Pays" where the caller paid to place a call to you (back when they charged you per minute to talk on a cell phone) but of course the cell company kept the money. But maybe cell companies could come up with something like that now but the customer gets the fee. For friends who call one another, it would cancel each others fees out over time but it would put scammers out of business.
Any unfamiliar senders get an autoreply asking for them to pay a fee to send the email. You as the receiver get paid this fee (-30%) for each email received (not read)