smart has no MX records.
Question and response
Question
dig smart. MX
Answer
The response has no answer records.
Authority
smart. 900 SOA ns0.centralnic.net. hostmaster.centralnic.net. 1773111966 60 1800 6048000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0