mailbackup.th.com has no MX records.
Question and response
Question
dig mailbackup.th.com. MX
Answer
The response has no answer records.
Authority
th.com. 3600 SOA ns.ksc.co.th. hostmaster.ns.ksc.co.th. 2026021200 3600 1200 129600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0