mx02.esn.at has no NS records.
NS records for this zone are defined at esn.at.
NS records for this zone are defined at esn.at.
Question and response
Question
dig mx02.esn.at. NS
Answer
The response has no answer records.
Authority
esn.at. 3600 SOA ns1-38.azure-dns.com. hostmaster.esn.at. 2015072776 3600 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0