g237.g48db3cf.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at g48db3cf.usw1.send.mailgun.net.
NS records for this zone are defined at g48db3cf.usw1.send.mailgun.net.
Question and response
Question
dig g237.g48db3cf.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
g48db3cf.usw1.send.mailgun.net. 300 SOA ns-cloud-b1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0