I was wondering does DH use Spamhaus?
from http://www.spamhaus.org/sbl/howtouse.html :
The Spamhaus Block List ("SBL") can be used by almost all modern mail servers, by setting your mail server's anti-spam DNSBL feature (sometimes called "Blacklist DNS Servers" or "RBL servers") to query sbl.spamhaus.org.
Exploits Block List
The Spamhaus Exploits Block List (XBL) is a realtime database of IP addresses of illegal 3rd party exploits, including open proxies (HTTP, socks, AnalogX, wingate, etc), worms/viruses with built-in spam engines, and other types of trojan-horse exploits.
SBL+XBL sbl-xbl.spamhaus.org 127.0.0.2|4|5|6 Combined zone to reduce queries. Includes both SBL and XBL zones