mail2.smartcluster.net has no NS records.
NS records for this zone are defined at smartcluster.net.
NS records for this zone are defined at smartcluster.net.
Question and response
Question
dig mail2.smartcluster.net. NS
Answer
The response has no answer records.
Authority
smartcluster.net. 900 SOA ns-312.awsdns-39.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0