ns2.mailinblue.com has no CNAME records.
Question and response
Question
dig ns2.mailinblue.com. NS
Answer
The response has no answer records.
Authority
mailinblue.com. 1561 SOA ben.ns.cloudflare.com. dns.cloudflare.com. 2394311118 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0