Preventing Spam Disguised as Error Mail

Some methods against spam are based on a principle that a recipient reads only messages from senders who are registered by the recipient (challenge and response). In these schemes, some exceptions are required to show error mail (bounce message) to a sender of an original message. However, spammers can abuse this exception to send spam to users. In this paper, we propose a new method which combines a Bayesian filter and challenge-and-response using Message Authentication Code (MAC) to avoid that spam.