mx.linje.dk has no CNAME records.
Question and response
Question
dig mx.linje.dk. NS
Answer
The response has no answer records.
Authority
linje.dk. 1631 SOA lucy.ns.cloudflare.com. dns.cloudflare.com. 2395210363 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0