Apex domains cannot have CNAME records.
Question and response
Question
dig mail-europe.com. NS
Answer
mail-europe.com. 5 NS oswald.ns.cloudflare.com.
mail-europe.com. 5 NS dayana.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0