This drives me NUTS. Email is insecure, but FAX is just FINE?!?!?
Actually, the best explanation I ever got for why I had to do it this way was that their receiving system was hard-config'd to only accept incoming documents from a fax-to-pdf conversion. It still blew my mind ('but I can give you a pdf... its RIGHT HERE!) but at least a) the person knew how the system worked, b) the person knew there was no way to insert data into that stream, and c) the person could explain parts a) and b) to me.
Things equal to nothing else are equal to each other.