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The original definition of a blacklist was a collection of entities or names that, for a specific, or a variety of reasons, may be denied a privilege, service, access, or mobility. In the near term, blacklist has come to mean a collection of URLs, IP addresses, or email addresses that have been flagged as spammers, malicious phishers, or other entities meant to do harm to a computer network, individual computer system, Intranet, and/or website.
In online computing, a blacklist controls access and most generally denies entry to a clearly defined range of users, programs, or network addresses. Simply put, it is part of a scripting process that actively monitors reports, from a wide range of internet sources, to determine the originator of unsolicited commercial or malicious email, commonly known as SPAM. Once these sources are identified they can be included in blacklist databases as a reference to create filters, and used to filter traffic for inbound mail servers, increasing security, and preventing SPAM from reaching users.
The lists most often used are compiled from open-relay or open proxy, and guilt-by-association lists. Open-relay and open proxy lists are hosted on blacklist servers, which act as the first in a line of access ports for network traffic, and in which all traffic is allowed to enter. These are based on open ports through which unauthorized network traffic is allowed to flow. Once the source of the messages are analyzed, they are then either allowed to be delivered or relegated to user’s spam or junk folders or summarily deleted and the user notified that a particular message was flagged and not allowed to be delivered.
For legitimate businesses and organizations, the way to not becoming flagged or added to a blacklist is to maintain clean and verified email addresses. This helps to ensure there will be a minimum of SPAM reports generated by email subscribers or recipients.
So who controls or maintains these lists? There are a variety of services, and in many cases the email service providers use a combination of lists generated by these independent sources and their own aggregated lists generated from user reports. Some of the more commonly used blacklist sites provide an automated tests that you can run against your IP address:
Blacklists are also contain blocks of IP addresses used by suspected sources and are known as “guilt by association” lists. This means that if a suspected SPAMMER owns an IP address that is close to another legitimate users address, they too will suffer an IP block. The legitimate sender will then begin to receive bounce-back emails from the destination domains and many times contain the reason for the denial of delivery. If this happens the user can then contact either the blacklist service directly and follow a series of requirements or procedures to be removed from the list. Another step that can be taken is to contact the owner of the domain that is blocking your email. It may also be necessary to report the problem to the domain that is subscribed to the blacklist service in order to let them know that the blacklist practices are generating complaints from their users. The mail administrator for any domain can be found by doing a WHOIS query with their registrar.
To avoid being blacklisted, maintain all security updates on the back end of network servers. On private systems keep anti-virus software up to date. These will help prevent systems from being used as a conduit through your connection by spammers who mask their identity by hiding behind yours.
For legitimate, high-volume email marketing by a business or organization, it is highly recommended to use an independent email marketing service that maintains clean lists by requiring their clients only accept subscriptions by a double opt-in system. These online email newsletter services continually monitor for suspected spammers entering their system and immediately block and terminate service. If, in the event that a client’s email newsletters are blocked by one or more email service providers, they can intervene and rectify the block quickly and efficiently.
