The problem in sending data files by e-mail is that standard e-mail can only handle files consisting of ASCII-characters which are described by 7 bit instead of 8 bit which are used by most file formats like programs and graphics files.
The solution is to convert 8 bit files to 7 bit files (causing a slight increase in the file size). There are several standards to do so. E.g. mime, uucode or binhex. E.g. if you are using a Mac software as your e-mail frontend it might encode your 8 bit file using binhex which is quite uncommon in the world of PCs and UNIX. You should check what kind of decoding the receiver can do. To many of us this underlying mechanism is unknown because encoding and decoding is done by the e-mail frontend and then confusion is great when it does not work. You will find on almost any system all of the above mentioned en-/decoding methods. So, sometimes it is necessary to decode "by hand" with an external program. But this doesn't explain why it worked in one case with jpg and gif files. - Daniel Roth
