a.nic.smart has no MX records.
Question and response
Question
dig a.nic.smart. MX
Answer
The response has no answer records.
Authority
nic.smart. 3600 SOA ns0.centralnic-dns.com. hostmaster.centralnic-dns.com. 1770996957 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0