Apex domains cannot have CNAME records.
Question and response
Question
dig a4mobility.it. NS
Answer
a4mobility.it. 5 NS ns2mi.infracom.it.
a4mobility.it. 5 NS ns1mi.infracom.it.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0