v550.v5b8b61bb.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at v5b8b61bb.usw1.send.mailgun.net.
NS records for this zone are defined at v5b8b61bb.usw1.send.mailgun.net.
Question and response
Question
dig v550.v5b8b61bb.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v5b8b61bb.usw1.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