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Here's process. A system is determined to be an open relay. It is added to one or more Blackhole lists. ISPs that subscribe to lists will bounce (return to sender) any messages that originate from open relay email system. This means ALL users from that email system are blocked. Every single one of them.
I know that seems cruel, but look at it this way. The open relay is encouraging spammers and is an unwitting accomplice in their operations. In fact, many of these open relays do not even know they are causing a problem, and first inkling that they get is when their users complain that things are running slowly or when problems occur with their servers.
The Blackhole lists are often run by individuals or small groups who believe in anti-spam cause. They are often unpaid volunteers who simply want to help clean up internet. They are also extraordinarily successful and many ISPs use their services.
To give you an idea of how successful this approach has been, there was a blackhole list called ORBZ. This was run by a young man named Ian Gulliver, a 20-year-old systems administrator from Ghent, New York. Ian is an extraordinary person and created one of most successful blackhole lists ever.
What ORBZ did is send messages to email systems to determine if they were open relays. If it determined that email system had this problem it added it to it's list. This was very successful until end of March, 2002.
At that time, ORBZ probed email server of Battle Creek, MI. Unfortunately, this system used Lotus email system, which has a known bug. The probe caused email server to slow down considerably, and it was interpreted by city as a hacker attack.
The poor ORBZ administrator found himself subject of a search warrant signed by a Michigan judge that authorized search and seizure of all data relating to ORBZ accounts.
Ian almost immediately shut down ORBZ system (he reopened service a few days later with some major changes and a new name), which led directly to a huge amount of spam suddenly being received all over internet. The closure of a single blackhole list had dramatic and noticeable results.
The upside is that blackhole lists prevent a tremendous amount of spam from getting sent throughout internet. They are very efficient and concept is simple and straightforward.
On downside, blackhole lists are not governed by anyone and answer to no one. They add open relays (and other spam sources) to their lists using their own rules, and usually assume suspected spammer is guilty until proven innocent.
They are, however, a necessary and vital piece in war against spam.
Richard Lowe Jr. is the webmaster of Internet Tips And Secrets at http://www.internet-tips.net - Visit our website any time to read over 1,000 complete FREE articles about how to improve your internet profits, enjoyment and knowledge.