Implement DNSBL checks

What are DNS Block Lists?
Also known as RBL - now trademarked
Lookup mechanism to see if an IP address is tainted
for nefarious activity 
as being a Dial-up address
Choices, choices
Open Relays
ORDB	http://www.ordb.org
RSL	http://relays.visi.com	Open Relays
Spam Sources
SBL	http://www.spamhaus.org
SPEWS	http://www.spews.org
CBL	http://cbl.abuseat.org
Open Proxies
Blitzed OPM	http://www.blitzed.org/opm/
Dynamic IPs
Sorbs DUHL	http://www.sorbs.net