mx0.ncuk.net has no CNAME records.
Question and response
Question
dig mx0.ncuk.net. NS
Answer
The response has no answer records.
Authority
ncuk.net. 1637 SOA ns0.ncuk.net. hostmaster.ncuk.com. 2026012602 7200 3600 1209600 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0