Apex domains cannot have CNAME records.
Question and response
Question
dig siriustec.it. NS
Answer
siriustec.it. 2 NS dns2.technorail.com.
siriustec.it. 2 NS dns4.arubadns.cz.
siriustec.it. 2 NS dns.technorail.com.
siriustec.it. 2 NS dns3.arubadns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0