Presumably you won't charge your friends to send you emails, so you'll need a rule that exempts people you've whitelisted.
Then there are the spammers, who won't adopt your system, so you'll never receive their emails, which is great.
But the other category of sender is companies that you want to send you a receipt or some other automated message when you enter your email address in an online form. No one is going to rewrite their forms to pay more money to send you messages you asked for, so unfortunately you'll have to give up on receiving such messages.
Hmm, so I guess you could implement the system you want with just a whitelist, and you don't need any crypto mining scheme at all.
