mx.foncor.ru has no NS records.
NS records for this zone are defined at foncor.ru.
NS records for this zone are defined at foncor.ru.
Question and response
Question
dig mx.foncor.ru. NS
Answer
The response has no answer records.
Authority
foncor.ru. 300 SOA ns1.edgedns.ru. support.edgecenter.ru. 1773403125 5400 3600 1209600 300
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0