incrediBILL - 9:05 pm on Jul 9, 2008 (gmt 0)

No, what you're thinking about is when you have your server's email daemon, like sendmail, set to the "paranoid" anti-spam function.

No, what I'm thinking of is a DNSBL [en.wikipedia.org].

If you do a query on 127.0.0.2 to see if it's good you do an NSLOOKUP for 2.0.0.127.dnsbl.example.com. If it returns NXDOMAIN then the site is OK, anything positive result (anything else) and it's bad.

If they're not doing this then the new incarnation is even lamer than I expected with horribly outdated information.

This can be used with email systems and other things.

Don't tell anyone (shhhhhh) because this is a unique application, but I actually use some of these DNSBL services to detect bad IPs and block visitors to my site if the results are positive.