Abstract
This paper proposes an anti-spam scheme that uses capability-based access control. In this scheme, rights to bypass spam filters are represented as capabilities, and an email message containing a valid capability bypasses the spam filter and goes straight to the receiver's inbox. As a result, the false positive problem inherent in existing spam filters is eliminated. This scheme allows a user to delegate rights to another person and is compatible with existing email systems and applications. It was implemented in an email client, Mozilla Thunderbird, along with a tool, capability basket, that provides an API for email clients and a graphical user interface (GUI) for users. This tool makes it easy for users to browse and distribute their capabilities. Capabilities are safely distributed by using an overlay network by the instant messenger Skype.