When Partner Portal users send email, unlike 'internal' users, an EmailMessages record is not created. While the text of the email is saved as an activity, there is only a text reference to the name of any attachments sent, the actual files are not saved.
This is a feature of Partner Portal.
While we can instruct users to upload the email attachments to a related record, this is not acceptable for audit and compliance.
Has anyone been able to resolve this issue?