mail1.jib.co.th has no CNAME records.
Question and response
Question
dig mail1.jib.co.th. NS
Answer
The response has no answer records.
Authority
jib.co.th. 1248 SOA pola.ns.cloudflare.com. dns.cloudflare.com. 2396754560 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0