mx.rvvnet.com has no NS records.
NS records for this zone are defined at rvvnet.com.
NS records for this zone are defined at rvvnet.com.
Question and response
Question
dig mx.rvvnet.com. NS
Answer
The response has no answer records.
Authority
rvvnet.com. 3600 SOA dns.rvvnet.com. hostmaster.rvvnet.com. 1177996632 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0