Every .dk domain that delegates its _acme-challenge name to 53866e58-76fc-4bbd-81d8-e84a339b5b0f.acme-dns.port4.de. 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.