The CBL takes its source data from very large mail server (SMTP) installations. Some of these are pure spamtrap servers, and some are not.
The CBL only lists IPs exhibiting characteristics which are specific to open proxies of various sorts (HTTP, socks, AnalogX, wingate, Bagle call-back proxies etc) and dedicated Spam BOTs (such as Cutwail, Rustock, Lethic, Kelihos etc) which have been abused to send spam, worms/viruses that do their own direct mail transmission, or some types of trojan-horse or "stealth" spamware, dictionary mail harvesters etc.
The CBL does not list based upon the volume of email from a given IP address.
The CBL also lists certain portions of botnet infrastructure, such as Spam BOT/virus infector download web sites, botnet infected machines, machines participating in DDOS, and other web sites or name servers primarily dedicated to the use of botnets. Considerable care is taken to avoid listing IP addresses that are shared or are likely to be shared with legitimate use, except in the case of infector download websites, phish emission or DDOS.
Our botnet detections may not necessarily directly involve the observation of spam emission, but most botnets are at least occasionally involved in email spam, in addition to infostealing, DDOS attacks etc.
In other words, the CBL only lists IPs that have attempted email connections to one of our servers in such a way as to indicate that the sending IP is infected with a spam-sending virus or worm, acting as a open proxy for the sending of spam, OR, IPs primarily used in the operation of botnets
The CBL does NO probes. In other words, the CBL NEVER makes connections to other machines to "test" anything.
The CBL does NOT test for nor list open SMTP relays.
The CBL only lists individual IPs, it NEVER lists ranges.
The CBL does NOT care whether an IP is dynamic or not, if connections the IP makes indicate that it's infected, it is listed regardless.
The CBL does NOT attempt to associate IP addresses to persons or organizations, and furthermore, a CBL listing should NOT be construed as accusing anyone of spamming - virtually all listees are the victims of a virus or other compromise, not deliberately spamming.
The CBL does NOT accept external submissions for listing. Hence it is not possible for the CBL to be used as an instrument of revenge (eg: "disgruntled ex-employee" or "competitor").
The CBL operates in an entirely automated way designed to avoid listings due to bounces of forged spam, virus bounces, and "real" mail servers emitting the occasional spam. However, in some circumstances severe mail server misconfiguration can make it look as if a mail server is infected.
It does not attempt to list every possible spam source.
This list is based on information believed to be reliable. No warranty is made that it is accurate or complete.... Use entirely at your own risk.
There is no supporting data or "evidence" file available for any given listing, and no mechanism to ask why any given listing took place. To counteract this, there is an automated no-questions-asked removals procedure allowing any affected party to delist a specific IP address rapidly. However, delisted IPs are relisted if new evidence of spam activity is subsequently detected.
Entries automatically expire after a period of time. The approximate detection time of a specific entry can be obtained from the web interface.