smtp2.pavietnam.com.vn has no MX records.
Question and response
Question
dig smtp2.pavietnam.com.vn. MX
Answer
The response has no answer records.
Authority
pavietnam.com.vn. 3600 SOA dnssec1.pavietnam.vn. hostmaster.pavietnam.com.vn. 2026030711 3600 7200 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0