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I wonder how he's going to find out just who is using RBL and who isn't?

Wouldn't it be easy enough to ping each suspect network from a machine that he knows has been RBL'd? Or (in the stealth scenario) send a message to an autoresponder on each suspected network?

identifying suspect networks would be hard, though.

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I wonder if he could subpeona the list of RBL subscribers in the interests of naming them in a law suit. Not that I think he has the financial backing to actually carry the suit out, but it is a curiosity.

yes, he could do that.

Look at the RBL site, a DNS subsciber it not tracked anywhere, except maybe Vixie's XFER log files. Even the MAPs crew doesn't know how many subscribers they have.

slight correction here: the subscribers number in the two hundred and twenties, and we know exactly who they are. noone AXFR's the zone without registering, or gets a BGP feed without registering. the thing we don't know how many we have of, is unsubscribed users who just add FEATURE(rbl) to their sendmail.mc files and never register at all. we've estimated this to be in the thousands or tens of thousands just based on the splay shown among query source addresses on the RBL.MAPS.VIX.COM nameservers, but a that's pretty rough way to estimate this quantity. -- Paul Vixie <paul@vix.com>