mx.proplex.ru has no NS records.
NS records for this zone are defined at proplex.ru.
NS records for this zone are defined at proplex.ru.
Question and response
Question
dig mx.proplex.ru. NS
Answer
The response has no answer records.
Authority
proplex.ru. 600 SOA ns3-l2.nic.ru. connect.proplex.ru. 2012041479 14400 3600 2592000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0