mta.smartape.net has no MX records.
Question and response
Question
dig mta.smartape.net. MX
Answer
The response has no answer records.
Authority
smartape.net. 3600 SOA ns3.smartape.net. abuse.smartape.net. 2013041697 3600 7200 2419200 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0