book.parcel.dhl.co.uk has no MX records.
Question and response
Question
dig book.parcel.dhl.co.uk. MX
Answer
The response has no answer records.
Authority
dhl.co.uk. 300 SOA ns4.dhl.com. netmaster.dhl.com. 2016112078 10800 3600 604800 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0