mx.retelit.net has no NS records.
NS records for this zone are defined at retelit.net.
NS records for this zone are defined at retelit.net.
Question and response
Question
dig mx.retelit.net. NS
Answer
The response has no answer records.
Authority
retelit.net. 300 SOA up.spin.it. hostmaster.spin.it. 2025033101 86400 7200 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0