Apex domains cannot have CNAME records.
Question and response
Question
dig mx2.nextpertise.nl. NS
Answer
mx2.nextpertise.nl. 3 NS dns1.spamrl.com.
mx2.nextpertise.nl. 3 NS dns2.spamrl.com.
mx2.nextpertise.nl. 3 NS dns3.spamrl.com.
mx2.nextpertise.nl. 3 NS dns4.spamrl.com.
Authority
The response has no authority records.
Additional
dns1.spamrl.com. 3 A 13.248.213.180
dns2.spamrl.com. 3 A 76.223.77.173
dns3.spamrl.com. 3 A 13.248.213.180
dns4.spamrl.com. 3 A 76.223.77.173
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0