An updated internet-draft is available from the IETF.
Abstract: «A protocol is shown which is highly spamresistant and can transparently be used as an extension of the regular email protocol. Accepted emails do the sender not cost money, not accepted ones do. A central server for keeping track of money and information is needed. A protocol, in which encryption naturally appear, is shown in which you can freely distribute your emailadress without ever having to read spam, for negligable costs.»
draft-kruithof-spam-reducing-02
Another Final Ultimate Solution to the Spam Problem. I really wish Vernon would add some anchors to his markup, to make it possible to link to an individual item (or in this case, items).