mx.37.230.91.in-addr.arpa has no NS records.
NS records for this zone are defined at 37.230.91.in-addr.arpa.
NS records for this zone are defined at 37.230.91.in-addr.arpa.
Question and response
Question
dig mx.37.230.91.in-addr.arpa. NS
Answer
The response has no answer records.
Authority
37.230.91.in-addr.arpa. 3600 SOA dns1.spider.pl. admin.ogicom.pl. 2011121019 10800 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0