You can separate DNS black lists into two categories: standard DNS Black Lists and trusted DNS Black Lists. A trusted DNS black list is one that you know is updated frequently, and is more likely to be accurate. You may also identify a black list as trusted because you find that for your uses it produces the least number of false positives. If a message matches one of these black lists, it is automatically deleted.
A standard DNS black list is a black list of which you are uncertain about its accuracy. If a message matches one of these lists, an X-Header is inserted into the message, indicating which black list it matched.
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