Apex domains cannot have CNAME records.
Question and response
Question
dig mxguardian.net. NS
Answer
mxguardian.net. 5 NS ns01.mxguardian.net.
mxguardian.net. 5 NS ns02.mxguardian.net.
Authority
The response has no authority records.
Additional
ns01.mxguardian.net. 5 A 52.22.28.218
ns02.mxguardian.net. 5 A 54.173.41.165
ns01.mxguardian.net. 5 AAAA 2600:1f18:260a:1a01:6257:2569:6920:6136
ns02.mxguardian.net. 5 AAAA 2600:1f18:260a:1a02:afb7:7ffb:cb0e:29b9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0