While China feels that centralization is the core of everything, and is licensing the use of mail servers to fight spam, thus totally ignoring the evolution of spam techniques, the other day I came across to some recent Spam Statistics from Oreilly.com -- scary numbers!
"Our mail servers accepted 1,438,909 connections, attempting to deliver 1,677,649 messages. We rejected 1,629,900 messages and accepted only 47,749 messages. That's a ratio of 1:34 accepted to rejected messages! Here is how the message rejections break down:
Bad HELO syntax: 393284
Sending mail server masquerades as our mail server: 126513
Rejected dictionary attacks: 22567
Rejected by SORBS black list: 262967
Rejected by SpamHaus black list: 342495
Rejected by local block list: 5717
Sender verify failed: 4525
Recipient verify failed (bad To: address): 287457
Attempted to relay: 5857
No subject: 176
Bad header syntax: 0
Spam rejected (score => 10): 42069
Viruses/malware rejected: 2575
Bad attachments rejected: 1594"
Draw up the conclusions for yourself, besides shooting into the dark or general syntax errors, total waste of email traffic resulting in delayed email is the biggest downsize here, thankfully, non-commercial methods are still capable of dealing with the problem. At the bottom line, sending a couple of million email messages on the cost of anything, and getting a minor response from a "Hey this is hell of a deal and has my username on the top of it!" type of end users seems to keep on motivating the sender. Localized spam is much more effective as an idea, but much easier to trace compared to mass-marketing approaches, though I feel it would emerge with the time.
Browse through Spamlinks.net for anything anti-spam related, quite an amazing resource.