mx-cluster-ca2-04.hornetsecurity.com has no CNAME records.
Question and response
Question
dig mx-cluster-ca2-04.hornetsecurity.com. NS
Answer
The response has no answer records.
Authority
hornetsecurity.com. 1660 SOA hank.ns.cloudflare.com. dns.cloudflare.com. 2398566758 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0