mx.ptl.ru has no NS records.
NS records for this zone are defined at ptl.ru.
NS records for this zone are defined at ptl.ru.
Question and response
Question
dig mx.ptl.ru. NS
Answer
The response has no answer records.
Authority
ptl.ru. 86400 SOA ns.quantum.ru. admin.quantum.ru. 202438349 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0