A spam blacklist is a listing of different Internet Protocol or IP addresses that are known to send out large amounts of unsolicited email. Lists of this type are often maintained on different servers, effectively blocking the delivery of emails from those IP addresses to any email client connected with that server. The idea is to reduce the amount of unsolicited emails that eventually reach end users. When used in conjunction with spam blocking software built into specific email programs, users usually find little to no spam delivered to their inboxes.
While different providers utilize slightly different criteria for spam blacklist configuration, most will set some type of limitation on the number of inbound copies of a single email that the server will deliver to its email clients. This is sometimes based on not only the number of copies of the same email that are simultaneously transmitted, but how often batches of that email are sent out. For example, if a server receives a total of 5,000 inbound emails with the same or similar subject lines originating from the same IP address, there is a good chance that the address will be added to the server’s spam blacklist.
One of the main benefits of using a spam blacklist on an email server is to minimize the amount of junk mail that filters through to end users. This in turn means less time wasted opening unsolicited emails that end users are ultimately not interested in receiving or reading in the first place. At the same time, rejecting emails that originated with IP addresses that are known to send out spam means that the server’s resources are not diverted from other essential tasks, which in turn maintains the efficiency of the server.
It is important to note that while a spam blacklist on a server will prevent a great deal of unsolicited email from filtering through, there is also the chance that the program will catch legitimate emails, such as a mass email sent out by a bonafide and approved vendor to all its customers. For this reason, many types of spam blacklist software include the option of identifying specific IP addresses or even a specific domain name that is to be allowed to pass through, no matter how many similar emails are received by the server within a given time frame. In addition, end users should make use of anti-spam software that is part of their email programs to filter emails that do pass through the server blacklist, making it possible to route undesirable emails directly into a spam folder and not clutter the user’s inbox.