Every .dk domain that delegates its _acme-challenge name to ac.f555c2a4dad8e6ea41bca7479121f2ce.norddb.dk.validate-akdv.net. Such CNAMEs hand DNS-01 certificate validation to a shared service, so this list shows who issues TLS certificates through it. Data comes from our own scanners, which re-resolve every .dk domain in the zone roughly once a week.