Experiences in building and operating ePOST, a reliable peer-to-peer application.

Peer-to-peer (p2p) technology can potentially be used to build highly reliable applications without a single point of failure. However, most of the existing applications, such as file sharing or web caching, have only moderate reliability demands. Without a challenging proving ground, it remains unclear whether the full potential of p2p systems can be realized.To provide such a proving ground, we have designed, deployed and operated a p2p-based email system. We chose email because users depend on it for their daily work and therefore place high demands on the availability and reliability of the service, as well as the durability, integrity, authenticity and privacy of their email. Our system, ePOST, has been actively used by a small group of participants for over two years.In this paper, we report the problems and pitfalls we encountered in this process. We were able to address some of them by applying known principles of system design, while others turned out to be novel and fundamental, requiring us to devise new solutions. Our findings can be used to guide the design of future reliable p2p systems and provide interesting new directions for future research.