How good are our weapons in the spam wars?

Will there ever be an end to "spam wars"? We are bombarded with unsolicited bulk email, we deploy newer and supposedly better ways of filtering spam, and yet spammers continue to devise creative ways to circumvent our defenses. Over the years, the volume of spam has increased steadily, in spite of the continued efforts to contain it. In order to understand the spam problem and to explore control methods, it is useful to analyze spam control techniques by looking at spam generation and transmission as a system. We find that not all spam control methods are equal, because each operates at different points in the system, where their leverage is widely different. In the end, no email control technique is likely to solve the spam problem definitively.