coremail01a.mail.zen.net.uk has no NS records.
NS records for this zone are defined at mail.zen.net.uk.
NS records for this zone are defined at mail.zen.net.uk.
Question and response
Question
dig coremail01a.mail.zen.net.uk. NS
Answer
The response has no answer records.
Authority
mail.zen.net.uk. 3600 SOA ns0.zen.co.uk. dnsmaster.zen.co.uk. 861 1800 120 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0