mail.ctigroupuk.com has no CNAME records.
Question and response
Question
dig mail.ctigroupuk.com. NS
Answer
The response has no answer records.
Authority
ctigroupuk.com. 9299 SOA ns1.eurodns.com. hostmaster.eurodns.com. 2025060300 86400 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0