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This plugin checks the reverse-DNS against a list of regular expressions. Any matches will result in a rejection, unless there is an allow rule to balance off broad regexes.

To give an example. Assume we add a rule to deny all hosts with dynamic in the rDNS hostname (.dynamic.). Now we find a mail server, that is clearly a false positive. We could try to correct the original regex (clearly it is a poorly written regex), or we could add an allow rule for (.*$). This means that even though the dynamic block rule matches, it will be superseded by the allow rule for


  • rdns.deny_regexps

    The list of regular expressions to deny. Over broad regexes in this list can be corrected by using the allow list.

  • rdns.allow_regexps

    The list of regular expressions to allow. This list is always processed in favor of rules in the deny file.

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