Comment by kbenson

I think it's a mistake to think of this as a long-standing policy for a spam blacklist. They are constantly evolving, just as the spam is, and there will be hiccups and problems as new detection techniques come online. At one point, identifying all domains listed in the content of definitively identified spam might have been very useful. Then spammers could have realized this and started peppering their content with random domains to poison this technique. In the short time between this technique being poisoned and discontinued (in this hypothetical scenario), quite a few people were probably affected, and while it was a short period, it would probably also account for 99% of the problems related to this.