mx.siel.si has no NS records.
NS records for this zone are defined at siel.si.
NS records for this zone are defined at siel.si.
Question and response
Question
dig mx.siel.si. NS
Answer
The response has no answer records.
Authority
siel.si. 1800 SOA dns1.siel.si. dns.siel.si. 1302 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0