Apex domains cannot have CNAME records.
Question and response
Question
dig mx4.emailsecurity.bracnet.net. NS
Answer
mx4.emailsecurity.bracnet.net. 5 NS dns2.spamrl.com.
mx4.emailsecurity.bracnet.net. 5 NS dns1.spamrl.com.
mx4.emailsecurity.bracnet.net. 5 NS dns4.spamrl.com.
mx4.emailsecurity.bracnet.net. 5 NS dns3.spamrl.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0