mx.tver.ertelecom.ru has no NS records.
NS records for this zone are defined at tver.ertelecom.ru.
NS records for this zone are defined at tver.ertelecom.ru.
Question and response
Question
dig mx.tver.ertelecom.ru. NS
Answer
The response has no answer records.
Authority
tver.ertelecom.ru. 3600 SOA ns8.ertelecom.ru. noc.ertelecom.ru. 2026020503 1800 180 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0