Apex domains cannot have CNAME records.
Question and response
Question
dig mailsafe.dk. NS
Answer
mailsafe.dk. 5 NS ns002.dnspilot.com.
mailsafe.dk. 5 NS ns003.dnspilot.com.
mailsafe.dk. 5 NS ns001.dnspilot.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0