Here is a thesis: the larger or more standardized the environmentfor sending messages, the more spam you should expect to get in orthrough it. Accordingly, email is heavily abused because it is hugelystandardized.

The spammer's motivation for abusing larger, standardized environmentsis obvious; the larger the environment, the more people you can reachwith a single technique, approach, or system. Larger environments havebetter return on effort, since generally (but not always) most of theeffort in spamming in an environment

Last time I mentioned that spammers wereperfectly capable of adopting their practices to defeat anti-spamheuristics like requiring a valid EHLO or reverse DNS, and so suchheuristics were, if effective and widely adopted, at best a temporaryfix. This raises an obvious corollary about good anti-spam heuristics.

Since spammers will adopt when it is both useful and possible, a goodanti-spam heuristic is some characteristic of the message or of how itis transmitted that the spammer cannot easily change. While people havemade various