Emails from a stamped individual could be "whitelisted" so as to no longer require a stamp to show up in your inbox. For instance, the first time you get an email from Amazon Prime (which they pay $0.001 cent to send), a box shows up saying "add this email to a whitelist so they don't have to spend money emailing you?"

As long as you earn more than a tenth of a cent for every email you send, you'll be fine. I don't think it's unfair to classify anything else as spam.