mx.vrxtraining.com has no NS records.
NS records for this zone are defined at vrxtraining.com.
NS records for this zone are defined at vrxtraining.com.
Question and response
Question
dig mx.vrxtraining.com. NS
Answer
The response has no answer records.
Authority
vrxtraining.com. 3600 SOA dns.vrxtraining.com. hostmaster.vrxtraining.com. 1659810824 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0