mx121215.superdata.vn has no CNAME records.
Question and response
Question
dig mx121215.superdata.vn. NS
Answer
The response has no answer records.
Authority
superdata.vn. 3600 SOA nsbak.dotvndns.com. hostmaster.superdata.vn. 2026022354 14400 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0