mail.dia-zbr.co.th has no MX records.
Question and response
Question
dig mail.dia-zbr.co.th. MX
Answer
The response has no answer records.
Authority
dia-zbr.co.th. 900 SOA ns2.ksc.net. admin.ns.ksc.co.th. 17 10800 3600 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0