mx4.mlrmr.com has no NS records.
NS records for this zone are defined at mlrmr.com.
NS records for this zone are defined at mlrmr.com.
Question and response
Question
dig mx4.mlrmr.com. NS
Answer
The response has no answer records.
Authority
mlrmr.com. 3301 SOA ns1.mail.ru. hostmaster.mail.ru. 3547405810 3600 300 604800 43200
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0