mail.tenuk.com has no NS records.
NS records for this zone are defined at tenuk.com.
NS records for this zone are defined at tenuk.com.
Question and response
Question
dig mail.tenuk.com. NS
Answer
The response has no answer records.
Authority
tenuk.com. 1800 SOA irma.ns.cloudflare.com. dns.cloudflare.com. 2397692336 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0