Apex domains cannot have CNAME records.
Question and response
Question
dig fastmail.gr. NS
Answer
fastmail.gr. 5 NS alina.ns.cloudflare.com.
fastmail.gr. 5 NS alec.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0