mx.dok3.ru has no NS records.
NS records for this zone are defined at dok3.ru.
NS records for this zone are defined at dok3.ru.
Question and response
Question
dig mx.dok3.ru. NS
Answer
The response has no answer records.
Authority
dok3.ru. 10800 SOA ns1.reg.ru. hostmaster.ns1.reg.ru. 1766060275 14400 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0