I was talking with G, our Cisco consultant about a networking issue I had when the talk turned to spam (as that's the root cause of all our email problems at The Company, which currently comprise half the issues in our trouble ticket system). One of the surprising bits of information G conveyed was that spammers are now using /16 network blocks for spamming.
A /16 network block is 65,636 consecutive IP addresses and are rather hard to come by (the smallest block ARIN will hand out is a /20, which gives 5,120 consecutive IPs and even then, you have to pay quite a bit and justify the usage of said block). The spammer then runs through the /16 (probably using 256, or a /24, the smallest routable block  at a time) until it's been blocked, and then sells it, or returns it; the spammer then obtains another /16 to abuse.
G also talked about other companies providing anti-spam techniques (like Barracuda) and the more he talked, the more I realized that spam is never going away—there's too much money to be made, by both sides.
Hypothetically speaking, if a spammer approached us and offered tons of money to use some of our IPs (we actually have a few /20s) to spam, if the money was good enough … well … the money would have to be mad money … and even then … well … everybody has their price. Anyway (this is a hypothetical situation) we made money to facility spamming. The spammer obviously makes money somehow or he wouldn't be doing this. The anti-spam companies like Barracuda make money by offering spam fitering services that need to be continuously updated.
So, what incentive is there for the commercial anti-spam companies to see spam eliminated completely? (as in, spammers never spam anymore)
Hmmm … sounds like anti-virus companies (not that I'm saying that anti-spam companies spam, but that their incentives are centered around staying in business, and totally eliminating spammers is not conducive to their remaining in business).
I only hope this is my more cynical side talking here, and not reality.
- Technically, the smallest routable block consists of four consecutive IP addresses (a /30). What I mean by “smallest routable block” in this context are routes that are accepted by the backbone routers.