Apex domains cannot have CNAME records.
Question and response
Question
dig mymailer.it. NS
Answer
mymailer.it. 5 NS ns103.ovh.net.
mymailer.it. 5 NS dns103.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0