Apex domains cannot have CNAME records.
Question and response
Question
dig cheetahmail.com. NS
Answer
cheetahmail.com. 5 NS ns-1812.awsdns-34.co.uk.
cheetahmail.com. 5 NS ns-835.awsdns-40.net.
cheetahmail.com. 5 NS ns-300.awsdns-37.com.
cheetahmail.com. 5 NS ns-1230.awsdns-25.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0