ddmrelay.smtpcorp.com has no CNAME records.
Question and response
Question
dig ddmrelay.smtpcorp.com. NS
Answer
The response has no answer records.
Authority
smtpcorp.com. 1800 SOA ada.ns.cloudflare.com. dns.cloudflare.com. 2397915257 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0