Apex domains cannot have CNAME records.
Question and response
Question
dig mailrouter.it. NS
Answer
mailrouter.it. 1 NS dns16.ovh.net.
mailrouter.it. 1 NS ns16.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0