ns3.dns-auth.net has no MX records.
Question and response
Question
dig ns3.dns-auth.net. MX
Answer
The response has no answer records.
Authority
dns-auth.net. 1800 SOA ns2.dns-auth.net. hostmaster.dns-auth.net. 2009111035 10800 1800 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0