Isn't robthebold's post good enough? Copy and paste that to a text file, rename it to .eml and email to yourself as attachment. You may need to add some Base64 content where he stripped it off. I can do that later today, gotta dash to work now.

EDIT: Just done. Replaced stripped attachments with random PDFs found on the web, otherwise left as robthebold's original. Saved as message.eml, sent as attachment to freemangordon, Bcc to myself.

A curious thing: Outlook can open the saved message.eml but not the one attached in the email. Like peterleinchen says, it shows there is an attachment in the list of emails, but nothing at all when I actually open that email. Jolla, in the same situation, shows there is an attachment "message.eml" and can download it but not open it. Testing on N900 needs to wait until I get back home.