mail.bestname.com.ua has no NS records.
NS records for this zone are defined at bestname.com.ua.
NS records for this zone are defined at bestname.com.ua.
Question and response
Question
dig mail.bestname.com.ua. NS
Answer
The response has no answer records.
Authority
bestname.com.ua. 600 SOA ns1.bestname.com.ua. domainmaster.bestname.com.ua. 2025123000 600 7200 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0