A Trust Based System for Enhanced Spam Filtering

The effectiveness of current anti-spam systems is limited by the ability of spammers to adapt to filtering techniques and the lack of incentive for mail servers to filter outgoing spam. A new approach, based on decentralised trust management, is described in this paper. An architecture and protocol, called TOPAS (Trust Overlay Protocol for Anti Spam), are presented. Each mail server records trust measures relating to each other mail server of which it is aware. Trust by one mail server in another is influenced by direct experience as well as recommendations issued by collaborating mail servers. The TOPAS protocol specifies how these experiences and recommendations are communicated between each spam filter and its associated trust manager, and between trust managers of different mail servers. A technique for improving mail filtering performance and the TOPAS protocol using these trust measures is also described. Finally, experimental work is presented that illustrates use of the protocol in a simulated network scenario. Initial results illustrate the dynamics of this system, and indicate the potential of this approach to significantly improve rates of false positives and false negatives in anti-spam systems. This is an extended version of a paper presented at the Availability, Reliability and Security Conference in April 2007 [1].