After forward attachment jpeg file from outlook to internal user, user is able to receive the email but not able to view the attachment

I'm currently performing migrate from Exchange 2007 to 2010 and weird thing happens.

External user send a jpeg file attachment to my customer, the 1st recipient is able to view the attachment. If the 1st recipient forward the jpeg file attachment to other internal user using HTML format, they are able to receive the email but not able to view the attachment. Unless the email is forward with plain text. After that, if the 2nd recipient forward the email to external users, the jpeg attachment is able to be seen

This weird things happen to everyone in the organization. You can view that the property shows there is a attachment and somehow it is not shown in Outlook. Really appreciate that someone can give some advise