mail.under.net.ua has no NS records.
NS records for this zone are defined at under.net.ua.
NS records for this zone are defined at under.net.ua.
Question and response
Question
dig mail.under.net.ua. NS
Answer
The response has no answer records.
Authority
under.net.ua. 1800 SOA kobe.ns.cloudflare.com. dns.cloudflare.com. 2398744355 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0