Zmail : Zero-Sum Free Market Control of Spam
The problem of spam is a classic "Tragedy of the commons". This paper proposes the Zmail protocol as a way to preserve email as a "Free" common resource for most users, while imposing enough cost on bulk mailers so that market forces will control the volume of spam. A key idea behind Zmail is that the most important resource consumed by email is not the transmission process but the end user's attention. Zmail requires the sender of an email to pay a small amount (called an "E-penny") which is paid directly to the receiver of the email.