mx253.secure-mailgateway.com has no CNAME records.
Question and response
Question
dig mx253.secure-mailgateway.com. NS
Answer
The response has no answer records.
Authority
secure-mailgateway.com. 9609 SOA a.ns14.net. info.secure-mailgateway.com. 2025092502 43200 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0