Spamhaus has just announced a new block list, the Domain Block List, here:
This is a great concept - it's designed to foil 'Snowshoe' spammers. Those are the folks who use a wide array of addresses to spam from, thus spreading out the spam load over hundreds or thousands of addresses - the same way a snowshoe spreads your weight out over the snow. It's very difficult to block, because they're constantly registering/spamming from/losing addresses.
But the spam payload is usually linked to a domain, and that's what the DBL is designed to block. The DBL is not an IP blocklist - it lists actual domains; it's not a normal RBL list. For this reason, you'll need SpamAssassin 3.31.
Now, the bad news - 3.31 isn't out yet. The minute it releases, I'll start testing this.
Spamhaus is the most solid, reliable set of blocklists out there, with an extremely low false positive rate. I can't wait to try this out.