sg.g1.rmailgateway.com has no NS records.
NS records for this zone are defined at g1.rmailgateway.com.
NS records for this zone are defined at g1.rmailgateway.com.
Question and response
Question
dig sg.g1.rmailgateway.com. NS
Answer
The response has no answer records.
Authority
g1.rmailgateway.com. 900 SOA ns-644.awsdns-16.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0