mx.itldc.net has no NS records.
NS records for this zone are defined at itldc.net.
NS records for this zone are defined at itldc.net.
Question and response
Question
dig mx.itldc.net. NS
Answer
The response has no answer records.
Authority
itldc.net. 3600 SOA ns.layer6.net. info.itldc.com. 2015100141 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0