The Passive Spam Block List
psbl.surriel.com, also known as The Passive Spam Block List, is a relatively new blacklist to the DNSBL scene. Like most other blacklists, pbsl.surriel.com uses spamtraps and honeypots to gather it's listing criteria. pbsl.surriel.com is an IP address based block list, and does not list URI's or URL's. At the time of this writing, more than 500,000 emails per day are used as part of the analytics process in determining if an IP address should be listed or not.
While any mail server can and will be listed, like other DNS blacklists, pbsl.surriel.com maintains an internal whitelist of host IP addresses that can never be listed. They also work with the well known dnswl.org to compare their lists to be sure a vetted whitelisted sender can not be listed. Somewhat unique to psbl.surriel.com is that upon listing, the tools provided to you for delisting offer data on how the initial listing was obtained. While the source address of the spamtrap that was sent to will not be revealed, significant information is given to aid in helping an email administrator track down the offending sender, and take action to make sure that a listing is not likely to happen again.
To become listed in the pbsl.surriel.com zone an email server must send an email to a spamtrap or honeypot address. At that time, the IP address of the sending server will be listed. Virus and bounce messages are filtered out of the system, leaving more than 99% of the listed addresses being confirmed as spam.
Use of this zone is like any other DNS blacklist. Have your email server query pbsl.surriel.com; any positive DNS response correlates with a listing.
Removal from pbsl.surriel.com is one of the simpler processes compared to other DNS blacklists. By requesting removal through the removal form, your IP address will be removed from the DNS database. This process generally takes about one hour. However, care should be taken to look at the listing criteria that was used to determine why it was deemed necessary to list your IP address. While removal is simple, it does not mean that you will not be listed again, if spam is again seen coming from your IP address.
The only other way to be removed from pbsl.surriel.com is through natural expiration. If no spam is seen coming from your IP address to an internal spam trap, in approximately two to three weeks the address will automatically expire from the system. According to pbsl.surriel.com, natural delisting is how more than 99% of their listings are removed. This can be interpreted into this being a high quality list with low false positives. Only aggressive spammers do not bother to work to have their IP address removed from a blacklist. If the majority of pbsl.surriel.com listings are naturally and automatically expiring, it is safe to conclude that the majority of the IP addresses are all spammers.