Interesting short-term antispam solution?

Everything Sysadmin has a good post on the subject of grey listing.

What it is? It's a way to set up a mail gateway or external mail server so that it handles emails a bit differently.

In a nutshell, it leverages normal behavior of spammers. They don't like to bother with retrying to send a message. Imagine you are trying to send a mass email to millions of people, even if it cuts down your sendthrough rate by 20%, you really can't afford the cycles worrying about who got the email and who didn't. Most of these guys (at least currently) just use a firehose approach to things, which is why it's such a nuisance in the first place.

So what grey listing does, is it causes your email server to spit back a "temporary" failure message, such as "server busy, please try again later" or some such. So most legitimate emailers will try again in 5 minutes or so and be let in. Whilst spammers won't try back at all. Or at least that's how it's supposed to work.

It won't replace more traditional methods like spam filters such as Spam Assassin, Postini (a host based filter that I really like) or Barracuda, but it will cut down on the amount of traffic that the spam filters have to deal with, if that's a concern for you.

As the title suggests, though, I think it's more of a short-term fix. Spammers, while they don't seem to get the message that we don't like them, do learn. So I won't be surprised if they start resending at least once as a rule.

This idea is interesting though as a study of the arms race between spammers and antispammers or even malware vs antimalware providers. As they use "social engineering" techniques to get more people to click through, the "anti" crowd use social engineering techniques as well to figure out the psychology/methodologies of these people/organizations to find weaknesses that can be exploited.

Unfortunately, the anti crowd is almost always in the reactionary position, the "black" side of the chessboard as it were and in these types of games, the advantage often goes to the "white" side of the chessboard. And no, the irony that the position of the bad vs good guys is reversed in relation to their color in this particular game of chess.