mail.utterfly.co.uk has no CNAME records.
Question and response
Question
dig mail.utterfly.co.uk. NS
Answer
The response has no answer records.
Authority
utterfly.co.uk. 1752 SOA carl.ns.cloudflare.com. dns.cloudflare.com. 2396916953 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0