I doubt very much if you can do this David, it goes against the whole idea of what a raw file is.
Rather than emailing it, you could use your internet service provider's web space (the vast majority of ISP accounts come with some web space for the user to utilise), and upload the raw file to a folder. You could then email your friend a link to the file where they could then download it from.
Contact your ISP, or take a good look around their home page, to find out about user web space, then get hold of a program such as the filezilla client
http://filezilla-project.org/
to upload your raw file.
Duncan