DNSWL

DNS-based whitelist (DNSWL) refers to a class of mechanisms in which domains or IP addresses are published in DNS to indicate that they are trusted sources. This approach is used primarily in email filtering to reduce false positives by allowing mailing domains that have been vetted to bypass or soften anti-spam checks. DNSWL entries are maintained by organizations that operate whitelist services, and are implemented by publishing records in a dedicated DNS zone or within the registrant’s own domain zone that can be queried by mail transfer agents.

When an MTA receives a message, it can perform a DNS query to determine whether the sender’s domain or IP is listed on a DNS whitelist. If the lookup succeeds, the server may route the message with a more favorable reputation score or skip certain checks; if not, the message is evaluated normally. The exact effect depends on the filtering policy of the recipient system and on the particular DNSWL service used.

DNSWL is commonly used to reduce false positives in email filtering, but similar techniques are used in other trust-based services where reputation data is distributed via DNS. The approach relies on the accuracy and reliability of the whitelist provider, as well as secure and timely DNS resolution. Misuse or compromised records can undermine trust by allowing unauthorized senders to bypass checks.

See also: DNS-based blacklists, domain reputation, email authentication.