What file format is needed to put digital audio in my out going emails?

I want to add back ground audio just as you would here it from the cd into my out going emails. I have tried to use *wma* and *mp3* formats, but I get a message saying that -one or more of the pictures could not be found and will not be included in the message-. So the other person recieving the message can not get the digital audio, but is able to get the pictures and text. I do not really want to use *midi* because then all the other person will get is a note. Is there any way to send my music as background into the outgoing emails? {with out having to attach them}