mail.ukr.host has no NS records.
NS records for this zone are defined at ukr.host.
NS records for this zone are defined at ukr.host.
Question and response
Question
dig mail.ukr.host. NS
Answer
The response has no answer records.
Authority
ukr.host. 1800 SOA adrian.ns.cloudflare.com. dns.cloudflare.com. 2398208257 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0