v5120.v508e7d51.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at v508e7d51.usw1.send.mailgun.net.
NS records for this zone are defined at v508e7d51.usw1.send.mailgun.net.
Question and response
Question
dig v5120.v508e7d51.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v508e7d51.usw1.send.mailgun.net. 300 SOA ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0