Fighting Spam by Breaking the Economy of Advertising by Unsolicited Emails

摘要

Unsolicited email (spam) is still a problem for users of the email service. Even though current email anti-spam solutions filter most spam emails, some still are delivered to the inbox of users. A special class of spam emails advertises websites, e.g., online dating sites or online pharmacies. The success rate of this kind of advertising is rather low, however, as sending an email does only involve minimal costs, even a very low success rate results in enough revenue such that this kind of advertising pays off. The anti-spam approach presented in this paper aims on increasing the costs for websites that are advertised by spam emails and on lowering the revenues from spam emails. Costs can be increased for a website by increasing traffic. Revenues can be decreased by making the website slow responding as some business gets lost. To increase costs and decreased revenues a decentralized peer-to-peer coordination mechanism is used to have mail clients to agree on a start date and time for an anti-spam campaign. During a campaign, all clients that received spam emails advertising a website send an opt-out request to this website. A huge number of opt-out requests results in increased traffic to this website and will likely result in a slower responsibility of the website. The coordination mechanism presented in this paper is based on a peer-to-peer mechanisms and a so-called paranoid trust model to avoid manipulation by spammers. A prototype implementation for the Thunderbird email client exist. The anti-spam approach presented in this paper breaks the economy of spam, hence, makes advertising by unsolicited emails unattractive.