sip.dotarai.com has no CNAME records.
Question and response
Question
dig sip.dotarai.com. NS
Answer
The response has no answer records.
Authority
dotarai.com. 1443 SOA ns.mail.in.th. hostmaster\.mail.in.th. 2026011329 86400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0