Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain  producedmoon.co.uk  by  mx.zohomail.com . [74.201.154.201].

The error that the other server returned was:
554 5.2.3 MailPolicy violation Error delivering to mailboxes

Why is this? They retried with all the large attachments gone and still the same? What is the problem? Can it be fixed quickly? 

Best, 

Leonie