mx.blackbeltlist.com has no NS records.
NS records for this zone are defined at blackbeltlist.com.
NS records for this zone are defined at blackbeltlist.com.
Question and response
Question
dig mx.blackbeltlist.com. NS
Answer
The response has no answer records.
Authority
blackbeltlist.com. 3600 SOA dns.blackbeltlist.com. hostmaster.blackbeltlist.com. 1537046158 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0