www.hornbill.com has no MX records.
Question and response
Question
dig group21.sites.hscoscdn20.net. MX
Answer
The response has no answer records.
Authority
hscoscdn20.net. 1800 SOA jerry.ns.cloudflare.com. dns.cloudflare.com. 2396679477 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0