DNSBL - Varieties of DNSBLs

Varieties of DNSBLs

In addition to the different types of listed entities (IP addressess for traditional DNSBLs, host and domain names for RHSBLs, URIs for URIBLs) there is a wide range of semantic variations between lists as to what a listing means. List maintainers themselves have been divided on the issues of whether their listings should be seen as statements of objective fact or subjective opinion and on how their lists should best be used. As a result, there is no definitive taxonomy for DNSBL's . Some names defined here (e.g. "Yellow" and "NoBL" ) are varieties that are not in widespread use and so the names themselves are not in widespread use, but should be recognized by many spam control specialists.

• White List - A listing is an affirmative indication of essentially absolute trust
• Black List - A listing is a negative indication of essentially absolute distrust
• Grey List - Most frequently seen as one word (greylist or greylisting) not involving DNSBL's directly, but using temporary deferral of mail from unfamiliar sources to allow for the development of a public reputation (such as DNSBL listings) or to discourage speed-focused spamming. Occasionally used to refer to actual DNSBL's on which listings denote distinct non-absolute levels and forms of trust or distrust.
• Yellow List - A listing indicates that the source is known to produce a mixture of spam and non-spam to a degree that makes checking other DNSBL's of any sort useless.
• NoBL List - A listing indicates that the source is believed to send no spam and should not be subjected to blacklist testing, but is not quite as trusted as a whitelisted source.