mx.granderiver.net has no NS records.
NS records for this zone are defined at granderiver.net.
NS records for this zone are defined at granderiver.net.
Question and response
Question
dig mx.granderiver.net. NS
Answer
The response has no answer records.
Authority
granderiver.net. 900 SOA nsb.vtx1.net. fieldopadmin.vtx1.net. 82 10800 3600 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0