mx2.vm.gin.ntt.net has no NS records.
NS records for this zone are defined at vm.gin.ntt.net.
NS records for this zone are defined at vm.gin.ntt.net.
Question and response
Question
dig mx2.vm.gin.ntt.net. NS
Answer
The response has no answer records.
Authority
vm.gin.ntt.net. 3600 SOA ipam01.sttlwa01.us.to.gin.ntt.net. dns-tech.gin.ntt.net. 2910 86400 3600 2592000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0