mx.vcn.com has no NS records.
NS records for this zone are defined at vcn.com.
NS records for this zone are defined at vcn.com.
Question and response
Question
dig mx.vcn.com. NS
Answer
The response has no answer records.
Authority
vcn.com. 86400 SOA ns1.vcn.com. root.vcn.com. 2026021904 10800 3600 1209600 86400
Additional
. 0 OPT ; payload 1432, xrcode 0, version 0, flags 0