mx2.wddonline.com has no NS records.
NS records for this zone are defined at wddonline.com.
NS records for this zone are defined at wddonline.com.
Question and response
Question
dig mx2.wddonline.com. NS
Answer
The response has no answer records.
Authority
wddonline.com. 900 SOA ns-1004.awsdns-61.net. awsdns-hostmaster.amazon.com. 2016072001 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0