mail.ecomsiam.com has no CNAME records.
Question and response
Question
dig mail.ecomsiam.com. NS
Answer
The response has no answer records.
Authority
ecomsiam.com. 10800 SOA ns.ecomsiam.com. info.ecomsiam.com. 2024121118 86400 7200 21600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0