auth.netnam.vn has no MX records.
Question and response
Question
dig auth.netnam.vn. MX
Answer
The response has no answer records.
Authority
netnam.vn. 3600 SOA ns1.netnam.vn. root.ns1.netnam.vn. 2008122960 28800 14400 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0