mail.GAZTELECOM.RU has no NS records.
NS records for this zone are defined at GAZTELECOM.RU.
NS records for this zone are defined at GAZTELECOM.RU.
Question and response
Question
dig mail.GAZTELECOM.RU. NS
Answer
The response has no answer records.
Authority
gaztelecom.ru. 3600 SOA ns.gaztelecom.ru. root.gaztelecom.ru. 2017081701 10800 3600 1209600 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0