Differences between DQS and Public Mirrors
While from the access technology perspective DQS is not particularly different from the DNSBL service provided by Spamhaus, there are a few important differences between the two one may want to be aware of.
While most of the data are the same, there are a few differences.
some SBL listings that are considered more prone to False Positives are not published on DQS
DQS records are served over DNS with a minimal 1s TTL (Time to Live) to ensure freshness of the response through caching DNS resolvers, while public mirrors serve data with a 60s TTL
DQS data are updated in realtime when new listings appear, unlike the public mirrors, that get only updated at scheduled intervals
some datasets are only available on DQS and will never be provided by public mirrors
access to public mirrors requires the use of a non-public, non-shared DNS resolver (therefore excluding services like Google Public DNS), while DQS can use any DNS channel
access to public mirrors can be inhibited anytime for a number of reasons, usually related with overquerying or observed malicious behavior from the querying network