mx4.limestonenetworks.com has no NS records.
NS records for this zone are defined at limestonenetworks.com.
NS records for this zone are defined at limestonenetworks.com.
Question and response
Question
dig mx4.limestonenetworks.com. NS
Answer
The response has no answer records.
Authority
limestonenetworks.com. 2560 SOA ns1.limestonenetworks.com. noc.limestonenetworks.com. 1772579306 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0