ghl0.ghlbf5d2fe.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at ghlbf5d2fe.usw1.send.mailgun.net.
NS records for this zone are defined at ghlbf5d2fe.usw1.send.mailgun.net.
Question and response
Question
dig ghl0.ghlbf5d2fe.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
ghlbf5d2fe.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