mx1.rockstable.it has no CNAME records.
Question and response
Question
dig mx1.rockstable.it. NS
Answer
The response has no answer records.
Authority
rockstable.it. 2941 SOA ns3.rockstable.org. hostmaster.rockstable.it. 2026012892 86400 3600 2419200 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0