Apex domains cannot have CNAME records.
Question and response
Question
dig rezmail.net. NS
Answer
rezmail.net. 5 NS ns03.red-spectrum.com.
rezmail.net. 5 NS ns04.rezmail.net.
Authority
The response has no authority records.
Additional
ns03.red-spectrum.com. 5 A 23.162.144.73
ns04.rezmail.net. 5 A 205.210.19.1
ns03.red-spectrum.com. 5 AAAA 2605:6340:0:15:0:0:0:3
ns04.rezmail.net. 5 AAAA 2605:4e40:0:401:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0