spf-send-list.cpu.co.uk has no MX records.
Question and response
Question
dig spf-send-list.cpu.co.uk. MX
Answer
The response has no answer records.
Authority
cpu.co.uk. 600 SOA ns1024.ui-dns.com. hostmaster.1und1.com. 2017060108 28800 7200 604800 600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0