mx-sender.cortel.cloud has no CNAME records.
Question and response
Question
dig mx-sender.cortel.cloud. NS
Answer
The response has no answer records.
Authority
cortel.cloud. 10800 SOA ns1.cortel.cloud. root.cortel.cloud. 2026020405 28800 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0