mail.tatcoop.com has no MX records.
Question and response
Question
dig mail.tatcoop.com. MX
Answer
The response has no answer records.
Authority
tatcoop.com. 300 SOA ns1.inet.co.th. root.tatcoop.com. 82 3600 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0