dns.smart has no MX records.
Question and response
Question
dig dns.smart. MX
Answer
The response has no answer records.
Authority
smart. 900 SOA ns0.centralnic.net. hostmaster.centralnic.net. 1773092336 60 1800 6048000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0