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