It appears that Elvis Daniel Velea <elvis@velea.eu> said:
There are a handful of blocklists that will list the whole block (that may be a /24 or even a /16) - Spamhaus is an example.
No, they don't. Spamhaus may expand a listing to a /24 or bigger when they see a pattern of abuse from a network but the SBL starts by listing one IP at a time. The XBL, which is run automatically, only lists individual IPs. They also have the PBL, Policy Block List, which lists ranges that the network operators say shouldn't be sending mail in the first place. Also keep in mind that "most blocklists" is meaningless. Any moron can run a blocklist, any many morons do. The vast majority of blockists are used by close to nobody, and only handful are widely enough used to matter. R's, John