mx2.retemetis.net has no CNAME records.
Question and response
Question
dig mx2.retemetis.net. NS
Answer
The response has no answer records.
Authority
retemetis.net. 10800 SOA dns1.retemetis.net. donato.conte.metissrl.it. 2025040700 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0