smtp.avmailer.ru has no NS records.
NS records for this zone are defined at avmailer.ru.
NS records for this zone are defined at avmailer.ru.
Question and response
Question
dig smtp.avmailer.ru. NS
Answer
The response has no answer records.
Authority
avmailer.ru. 3600 SOA avmailer.ru. info.avmailer.ru. 2021032321 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0