E-mail retrieval is becoming increasingly expensive in today’s world. The expense is incurred by the receipient rather than the sender. The expense is more in terms of loss of time, bandwidth & productivity.
Spam filters are merely a workaround to solve this problem. Research projects such as Penny Black project are aimed at resolving the spam problem by attacking the root cause.
In a nutshell, the idea is this: “If I don’t know you, and you want to send me mail, then you must prove to me that you have expended a certain amount of effort, just for me and just for this message.” The approach is fundamentally an economic one. Suppose we measure effort in CPU cycles. Since there are about 80,000 seconds in a day, a computational “price” of just ten seconds per message would limit a spamming computer to at most 8,000 messages daily. So spammers would have to invest heavily in hardware in order to send high volumes of spam.
Four Stanford undergraduates, under the supervision of Dan Boneh, implemented the computational approach using a very simple proxy architecture. The research component of this project is largely complete & the researchers continue to investigate how these ideas might be realized in practice.
Reference
http://research.microsoft.com/research/sv/PennyBlack/demo/index.html
http://research.microsoft.com/research/sv/PennyBlack/
Information Technology