v598.v54c35a42.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at v54c35a42.usw1.send.mailgun.net.
NS records for this zone are defined at v54c35a42.usw1.send.mailgun.net.
Question and response
Question
dig v598.v54c35a42.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v54c35a42.usw1.send.mailgun.net. 300 SOA ns-cloud-a1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0