Apex domains cannot have CNAME records.
Question and response
Question
dig serverlet.it. NS
Answer
serverlet.it. 5 NS ns3.serverlet.it.
serverlet.it. 5 NS ns2.serverlet.com.
serverlet.it. 5 NS ns1.serverlet.com.
Authority
The response has no authority records.
Additional
ns3.serverlet.it. 5 A 130.185.108.70
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0