mx1.netart.com has no NS records.
NS records for this zone are defined at netart.com.
NS records for this zone are defined at netart.com.
Question and response
Question
dig mx1.netart.com. NS
Answer
The response has no answer records.
Authority
netart.com. 3600 SOA ns1.netart.com. office.netart.com. 2008133200 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0