Policies for sending archived attachments

I have a situation where we use the preview pane in Outlook and use EX 4.8 to archived docs. The issue is that if a user "forwards" the email without opening the email first the user on the other end gets the message "You must first open the email..." the attachment is not sent.


If you open the email then press forward first everything works.

How are customers handling this issue: Written Policy/Training/etc?