Apex domains cannot have CNAME records.
Question and response
Question
dig mx4.divinet.nl. NS
Answer
mx4.divinet.nl. 4 NS dns2.spamrl.com.
mx4.divinet.nl. 4 NS dns3.spamrl.com.
mx4.divinet.nl. 4 NS dns4.spamrl.com.
mx4.divinet.nl. 4 NS dns1.spamrl.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0