mail.servers.ru has no NS records.
NS records for this zone are defined at servers.ru.
NS records for this zone are defined at servers.ru.
Question and response
Question
dig mail.servers.ru. NS
Answer
The response has no answer records.
Authority
servers.ru. 30 SOA ns1.srvdns.ru. noc.exepto.ru. 2026031201 60 30 604800 30
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0