Apex domains cannot have CNAME records.
Question and response
Question
dig orangemail.cm. NS
Answer
orangemail.cm. 5 NS douala0.orange.cm.
orangemail.cm. 5 NS yaounde0.orange.cm.
Authority
The response has no authority records.
Additional
douala0.orange.cm. 5 A 41.202.217.13
yaounde0.orange.cm. 5 A 41.202.217.135
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0