v528.v5f9d002f.use4.send.mailgun.net has no NS records.
NS records for this zone are defined at v5f9d002f.use4.send.mailgun.net.
NS records for this zone are defined at v5f9d002f.use4.send.mailgun.net.
Question and response
Question
dig v528.v5f9d002f.use4.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v5f9d002f.use4.send.mailgun.net. 300 SOA ns-cloud-d1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0