Over on his blog, Justin Mason shows us how you can re-run already received messages through SpamAssassin. This is a neat idea. He explains this in the context of coming back from vacation, and having a big pile o' messages to wade through. A lot of that is going to be spam that got by the spam filter, because various sending IPs and link URIs weren't yet blacklisted. On the theory that they may now be blacklisted, why not run it all through SpamAssassin one more time, and see if it finds more of the spam? It's a solid theory, and based on my various blacklist tests, I do know that a delay can help improve the hit rate of any DNSBL or URIBL.