摘要： The e-mail system is one of the most common communication platforms these days. The term spam refers to
unsolicited bulk e-mail that people do not want to receive. Today, it is gradually becoming a serious problem that results
in significant costs both to e-mail recipients and to ISPs (Internet Service Providers). Furthermore, spam may open the
door to security and privacy threats. More and more people have become concerned about the issue and are making efforts
to develop various anti-spam approaches, some of which are in-process proposals, while others are currently in use. In this
article, we analyze key anti-spam approaches, including filtering, remailers, e-postage, Hashcash, and sender authentication.
We discuss their advantages and disadvantages in various aspects. Furthermore, we define our evaluation criteria and
compare the anti-spam approaches based on those criteria. These include: cost to adopt, cost for standards and infrastructures,
robustness, effectiveness in reducing spam, user convenience and transparency, and e-mail transferring performance.
We believe that this paper can serve as a basis for improving existing anti-spam techniques and for exploring the optimum
solutions to combating spam in the future. Technical details of each anti-spam approach are not discussed in-depth
in this article because of space limitations.
