The package used a little while ago in an article explaining
how to check the spam blacklists has recently been updated.
Net_DNSBL 1.2.1 is now available. It looks like there haven't been any big changes but if you want the latest and greatest feel free to update.
Taking a look at the trackbacks to the package brings up an
interesting article looking at doing the same thing as in my article but from the perspective of someone running their own smtp server.