mail.old.avmailer.ru has no NS records.
NS records for this zone are defined at old.avmailer.ru.
NS records for this zone are defined at old.avmailer.ru.
Question and response
Question
dig mail.old.avmailer.ru. NS
Answer
The response has no answer records.
Authority
old.avmailer.ru. 3600 SOA avmailer.ru. info.avmailer.ru. 2021040104 3600 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0