Also, it won't be hl.co.uk that is actually sending the email.

The message headers show that it is actually adobe.net infrastructure that is sending the email. So the mail will be coming from their Marketo email marketing automation system. The only way hl.co.uk will be involved is with setting up DNS records correctly to allow adobe.net/Marketo to deliver mail on their behalf.

For my sins, I've worked on projects using both Marketo and their competition Marketing Cloud to deliver both transactional and marketing email