mail.SN.RU has no NS records.
NS records for this zone are defined at SN.RU.
NS records for this zone are defined at SN.RU.
Question and response
Question
dig mail.SN.RU. NS
Answer
The response has no answer records.
Authority
SN.RU. 86400 SOA ns5.salenames.RU. noc.salenames.RU. 2025111801 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0