Every .dk domain that delegates its _acme-challenge name to f51c0a22-c6ea-491c-a261-115f1db26b87.auth.acme-challenge.dk. 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.