Apex domains cannot have CNAME records.
Question and response
Question
dig celestemail.com. NS
Answer
celestemail.com. 2 NS ns1.celeste.fr.
celestemail.com. 2 NS ns2.celeste.fr.
celestemail.com. 2 NS ns3.celeste.fr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0