>>681
以下を読むと対botnetに効果絶大な気がします。一度試して欲しいです。
http://www.dnsbl.info/dnsbl-details.php?dnsbl=b.barracudacentral.org
When email is received, the connection is automatically analyzed to determine if the connecting machine is either an open proxy or a node in a spam-generating botnet.
If either is true, the IP address is immediately added to the Barracuda Reputation Block List (BRBL). The BRBL only lists single IP addresses.