Apex domains cannot have CNAME records.
Question and response
Question
dig dnmailer.net. NS
Answer
dnmailer.net. 5 NS ns2.viidakko.fi.
dnmailer.net. 5 NS ns3.viidakko.net.
dnmailer.net. 5 NS ns4.viidakko.net.
dnmailer.net. 5 NS ns1.viidakko.fi.
Authority
The response has no authority records.
Additional
ns3.viidakko.net. 5 A 162.159.26.4
ns4.viidakko.net. 5 A 199.247.155.53
ns3.viidakko.net. 5 AAAA 2400:cb00:2049:1:0:0:a29f:1a04
ns4.viidakko.net. 5 AAAA 2620:111:8007:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0