ns1.luadns.net has no MX records.
Question and response
Question
dig ns1.luadns.net. MX
Answer
The response has no answer records.
Authority
luadns.net. 3600 SOA ns1.luadns.net. hostmaster.luadns.com. 1770836192 1200 120 604800 3600
Additional
. 32768 OPT ; payload 512, xrcode 0, version 0, flags 32768