From: "Simon Byrnand"
[half hearted effort to block spam] (And in that category I include manual blocking of huge swarths of ip space, outright blocking based on most RBL blacklists, Mailmarshall, and Challenge response systems, all of which have unacceptable collateral damage
Well said.
I recently dealt with an ISP in the US who had blocked 202.0.0.0/8 (!) because "all we ever get from that netblock is spam from China".
And there is the issue. If ISPs use network blocking as a mechanism to block Spam then the ultimate outcome will be be a block on all networks and zero email delivery. A human being can scan down 20 emails in their Inbox and immediately descriminate between Spam and valid email because they have an educated eye and brain. A Spam filter can do the same, but first you have to educate it. Put the effort into training the filter and it will perform better than a human being. Cheers BG.