mobile-mail02.a8.net has no NS records.
NS records for this zone are defined at a8.net.
NS records for this zone are defined at a8.net.
Question and response
Question
dig mobile-mail02.a8.net. NS
Answer
The response has no answer records.
Authority
a8.net. 900 SOA ns-124.awsdns-15.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0