The only way to stop spam is to charge to send an email.
The most idiotic idea this year.
Microsoft has/had an interesting solution to spam that runs along the lines of your solution: Every time you send e-mail, the receiving e-mail server refuses the e-mail unless your e-mail server provides the solution to a complex mathematical problem. IOW, the sending e-mail server must use computing horsepower to solve the problem and provide the receiving server the correct answer. The whole process might take a few seconds of processor time. For the two, three, four e-mails you and I send every day this would be no problem; in fact, we wouldn't notice. But for the spammer, who's sending millions of e-mails a day, it would bring his business down because he wouldn't have the computing horsepower to keep up with his volume of sent e-mail.
I don't know where this solution lies today. I heard about it about a year ago.
I just change my email address every few days. That seems to do the trick.
That's an old canard already, and no more true for wear. It costs money to send a fax but fax machines still get spammed like there is no tomorrow.
If you charge for sending email, what will happen in actuality is that the spammers will make zero change to what they already do, and the people whose addresses they spoof as the return addresses will end up with bills for millions upon millions of emails that they didn't send.
The way to stop spam is to institute draconian punishment for the ones we do catch, 20 year sentences for individuals and total confiscation of the assets of companies which use spam as advertising.