v50.v54767b5a.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at v54767b5a.usw1.send.mailgun.net.
NS records for this zone are defined at v54767b5a.usw1.send.mailgun.net.
Question and response
Question
dig v50.v54767b5a.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v54767b5a.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