aws-smtp.osgbilling.com has no NS records.
NS records for this zone are defined at osgbilling.com.
NS records for this zone are defined at osgbilling.com.
Question and response
Question
dig aws-smtp.osgbilling.com. NS
Answer
The response has no answer records.
Authority
osgbilling.com. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2009011100 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0