smtpb.leonet.it has no CNAME records.
Question and response
Question
dig smtpb.leonet.it. NS
Answer
The response has no answer records.
Authority
leonet.it. 1759 SOA ns1.leonet.it. hostmaster.leonet.it. 2026022702 3600 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0