An uptick in spam has me looking for a way to score mail coming from sites that use "anonymous whois" services, i.e., services that register domain names on behalf of others to hide their identities.
I found an RBL (domain name lookup only, not IP addresses) at Anonymous Whois List. The page provides SpamAssassin rules for usage, to look in URLs in the body of a message. That's not bad, but I'd also like to use it to look at the delivering SMTP server's WHOIS registration., similar in concept to using urirhsbl as part of a header rule. But I'm not sure that's possible.
So I'm just throwing this out there to see if anyone has used this RBL, including writing custom rules for header lookups.