v5216.v51a3e4cb.usw1.send.mailgun.net has no NS records.
NS records for this zone are defined at v51a3e4cb.usw1.send.mailgun.net.
NS records for this zone are defined at v51a3e4cb.usw1.send.mailgun.net.
Question and response
Question
dig v5216.v51a3e4cb.usw1.send.mailgun.net. NS
Answer
The response has no answer records.
Authority
v51a3e4cb.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