mx1.krystal.uk has no CNAME records.
Question and response
Question
dig mx1.krystal.uk. NS
Answer
The response has no answer records.
Authority
krystal.uk. 10800 SOA ns1.krystal.co.uk. admin.krystal.co.uk. 2026022300 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0