mail19.thaibombmail.com has no CNAME records.
Question and response
Question
dig mail19.thaibombmail.com. NS
Answer
The response has no answer records.
Authority
thaibombmail.com. 1800 SOA beth.ns.cloudflare.com. dns.cloudflare.com. 2394203620 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0