Apex domains cannot have CNAME records.
Question and response
Question
dig mailvox.it. NS
Answer
mailvox.it. 5 NS ns15.ovh.net.
mailvox.it. 5 NS dns15.ovh.net.
Authority
The response has no authority records.
Additional
ns15.ovh.net. 2 A 5.39.114.9
dns15.ovh.net. 2 A 5.135.110.101
ns15.ovh.net. 2 AAAA 2001:41d0:b00:ee00:0:0:0:2
dns15.ovh.net. 2 AAAA 2001:41d0:d00:f400:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0