Apex domains cannot have CNAME records.
Question and response
Question
dig infosecmail.net. NS
Answer
infosecmail.net. 5 NS ns-2018.awsdns-60.co.uk.
infosecmail.net. 5 NS ns-129.awsdns-16.com.
infosecmail.net. 5 NS ns-840.awsdns-41.net.
infosecmail.net. 5 NS ns-1094.awsdns-08.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0