v53.v5b53cb91.use4.send.mailgun.net has no NS records.
NS records for this zone are defined at v5b53cb91.use4.send.mailgun.net.
NS records for this zone are defined at v5b53cb91.use4.send.mailgun.net.
Question and response
Question
dig v53.v5b53cb91.use4.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v5b53cb91.use4.send.mailgun.net. 300 SOA ns-cloud-e1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0