mx1.mgn.net has no NS records.
NS records for this zone are defined at mgn.net.
NS records for this zone are defined at mgn.net.
Question and response
Question
dig mx1.mgn.net. NS
Answer
The response has no answer records.
Authority
mgn.net. 60 SOA ns-1309.awsdns-35.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0