mx2.smartape.net has no NS records.
NS records for this zone are defined at smartape.net.
NS records for this zone are defined at smartape.net.
Question and response
Question
dig mx2.smartape.net. NS
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