dk.mx2.mx25.net has no NS records.
NS records for this zone are defined at mx25.net.
NS records for this zone are defined at mx25.net.
Question and response
Question
dig dk.mx2.mx25.net. NS
Answer
The response has no answer records.
Authority
mx25.net. 3600 SOA dns1.p01.nsone.net. hostmaster.nsone.net. 1726073215 10000 1800 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0