The BlarsBL is maintained by Blars at his wim. Use for any purpouse should be done at your own risk, and Blars is not responsible for use by anyone but himself.
In general, an entire netblock is added rather than just a single IP or customer of a larger ISP. (For example, if hugeisp has a /16 that they allocate a single /24 to spamcustomer, the /16 will be listed rather than just the /24.) An entire ISP may be added if they show a pattern of rejecting valid spam complaints for invalid reasons.
This is not a low collateral damage list. If you buy services of spam support service (even if it isn't their primary business) you should expect to be listed eventually. For non-spammers this can be considered an early warning, since few people use BlarsBL to block email. SPEWS also lists netblocks of spam support organizations, and is much more widly used to block email. Just listing spammers doesn't work, the ISP will just move the spammer to a non-listed address and the non-spamming customers have no incentive to force their ISP to reform.
Areas of the world that have a strong pattern of never acting on spam complaints may have blocks listed on BlarsBL with a single spam from their netblock. (Currently, this is Asia and South America.) ISPs (with at least a /18 block) in these areas with working abuse addresses in their whois data may contact Blars and ask to be an exception to this policy.
Listings are mostly based on spam received at blars.org and selected other addresses. If the IP block has a working abuse address (see below), it will take either repeated inaction on a single spammer or a pattern of spammers to get a listing. Being done by a human, the boundaries are somewhat fuzzy.
The reason for adding to BlarsBL is encoded in the two least significant bytes of the returned address: (Listed least significant bit first.)
Since MAPS has gone commercial, entries with .4 are no longer being added. If a non-commercial reasonably complete list of dynamic addresses is found, .4 will be redefined.
No working abuse address (.16) is based on the IP address's whois entry. (It's their block that will be listed.) Besides not being able to figure an appropriate address out from the whois entry or direct bounces, indirect bounces and vacataion replies are also counted. (If your abuse department is on vacation, you should shut down your routers.)
The "sued or prosecuted DNSBL provider" (1.) is for listing blocks that contain orginizations that sued MAPS, did criminal prosecution of ORBZ, and such cases.
A DOS (denial of service) attack listing (2.) is for systems that attack one of my systems. Broken mail software that retries abusivly when it gets a SMTP 4xx return code is the most common reason, but abuse of DNS servers is also counted. This generally will get a /24 listed, unless it's the ISPs servers that are doing the abuse.
Spamware suppliers have to bring themseves to Blars' attention to get a 4. listing. Spamming adds for spamware is the normal way.
Knowingly supporting spammers (8.) includes such things as refusing to act on complaints about hosted web pages "because the mail didn't come from us".
Legal ("cartoony") threats may get your site listed as 16., and may be posted publicly.
Attempting to relay mail through my system or access a (nonexistant) formmail script will get the /24 associated as 32. and 64. respectivly. Administrators running publicly accessable DNSBL lists of exploitable systems may send me email asking your checker to be unlisted.
BlarsBL is located at block.blars.org. Do the usual prepending of the reversed quad IP address. Zone transfers are not allowed without prior arangement. DNS secondaries are not being sought at this time. Please do not abuse this service, more than 1000 queries per day from a single site is considered such abuse. If you plan on such heavy use of BlarsBL, please contact Blars and arrange to become a DNS secondary.
The 127.0.0.2 test address is now supported. It will return a code with many bits set.
If you would like a site be added or removed from BlarsBL, you may hire Blars at his normal consulting rates (currently $250/hour, 2 hour minimum, $1000 deposit due in advance for non-established customers) to investigate your evidence about the site. If it is found that the entry was a mistake, no charge will be made and the entire deposit will be refunded. Send Blars email from a non-listed account to verify current rates and arrange payment.