mx01.fibianet.dk has no CNAME records.
Question and response
Question
dig mx01.fibianet.dk. NS
Answer
The response has no answer records.
Authority
fibianet.dk. 244 SOA ns1.fibianet.dk. hostmaster.fibia.dk. 2026022506 21600 3600 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0