Data Query Service (DQS)

Spamhaus databases are traditionally consulted through DNS queries, where the object to be queried (an IP or a domain/hostname) is prepended to a DNSBL domain zone.

This scheme has been in use for decades and is thoroughly supported across the mailserver industry, where it became a standard due to its lightweight nature and ease of implementation, to the point of being formalized in RFC5782.

Spamhaus Data Query Service (DQS) is simply an implementation of it, with only minor details distinguishing it from most others.