mx.hubapi.com has no NS records.
NS records for this zone are defined at hubapi.com.
NS records for this zone are defined at hubapi.com.
Question and response
Question
dig mx.hubapi.com. NS
Answer
The response has no answer records.
Authority
hubapi.com. 1800 SOA jerry.ns.cloudflare.com. dns.cloudflare.com. 2397369296 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0