smtp031.mx.imdlv.net has no NS records.
NS records for this zone are defined at imdlv.net.
NS records for this zone are defined at imdlv.net.
Question and response
Question
dig smtp031.mx.imdlv.net. NS
Answer
The response has no answer records.
Authority
imdlv.net. 1800 SOA ns1.digitalocean.com. hostmaster.imdlv.net. 1774743348 10800 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0