Apex domains cannot have CNAME records.
Question and response
Question
dig spamfilteringcloud.com. NS
Answer
spamfilteringcloud.com. 4 NS ns0.cyberlynk.net.
spamfilteringcloud.com. 4 NS ns.cyberlynk.net.
Authority
The response has no authority records.
Additional
ns.CYBERLYNK.NET. 4 A 66.185.17.218
ns0.CYBERLYNK.NET. 4 A 66.185.25.210
ns.CYBERLYNK.NET. 4 AAAA 2605:3800:0:56:0:0:0:10
ns0.CYBERLYNK.NET. 4 AAAA 2605:3800:0:44:0:0:0:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0