How can I view an attachment in an email that is within a thread?

Issue
An email is showing the attachment icon on the document list but opening the email and expanding the Threads section, this shows as ''No available attachments''.

Cause
This is because the way the email was originally created and filed (including the attachments) as a thread.

Solution
The only way to preview these attachments is using Export (refer to Exporting Documents) and to look at the attachments in the downloaded email.