Every .dk domain whose MX record points to 53bp3dbcbmc4ikkxz7cugbiiab4h5y6raph6sqnq2e7vxeklhyta.mx-verification.google.com. Mail-server reverse lookups show which organisations share a mail provider and how widely a hosted mail platform is used. Data comes from our own scanners, which re-resolve every .dk domain in the zone roughly once a week.