mx2.dotvndns.vn has no CNAME records.
Question and response
Question
dig mx2.dotvndns.vn. NS
Answer
The response has no answer records.
Authority
dotvndns.vn. 2958 SOA ns1.dotvndns.vn. hostmaster.dotvndns.vn. 2025120203 14400 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0