mx0.bbtnetworks.com has no NS records.
NS records for this zone are defined at bbtnetworks.com.
NS records for this zone are defined at bbtnetworks.com.
Question and response
Question
dig mx0.bbtnetworks.com. NS
Answer
The response has no answer records.
Authority
bbtnetworks.com. 300 SOA ns-cloud-a1.googledomains.com. cloud-dns-hostmaster.google.com. 36 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0