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DNSWL (DNS-based whitelist) is both a generic term and a specific list. The specific list DNSWL.org, lists over 50,000 legitimate SMTP senders[1].


Generic need for whitelisting

Natural language understanding is not a mature field. Common computer processes used for spam filtering apply heuristics to avoid presenting too many useless messages to email recipients. This has the severe impact of reducing SMTP reliability[2] by creating false positives, i.e. silently dropping legitimate messages. Whitelists tackle the task of vouching for a sender, which implies identifying an accountable party that the sender belongs to.


DNSWL.org has been founded on 1st November 2006 by Matthias Leisi[3]. Legitimate senders can register for free. Most DNS servers are sponsored by various organizations worldwide[4].

DNSWL.org lists IP addresses, but also hold domain names, category, and email contact addresses. Each IP address is given a "trustworthiness" level; applications, e.g. SpamAssassin, typically decrease the "spamminess" score of a message by a value proportional to that level.

See also


  1. Matthias Leisi (27 January 2009). "50'000!". http://www.dnswl.org/news/archives/10-50000!.html. Retrieved 16 July 2009. 
  2. See Bounce message for a discussion about delivery errors, and Backscatter (e-mail) for why they cannot always be noticed to the sender.
  3. Matthias Leisi (1 November 2008). "Happy Birthday, dnswl.org". http://matthias.leisi.net/archives/189-Happy-Birthday,-dnswl.org.html. Retrieved 16 July 2009. 
  4. DNSWL's thanks page doesn't list its sponsors extensively. Robtex's page and whois data at PIR.org are more up to date.

External links


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