What format your music is in will probably determine which method of transfering is easiest for you. if they are sound recordings - .wav; .au; even mp3 (which are smaller) - Clinton's suggestion or a similar setup would probably be best.

Images can also clog a mailbox and are often best treated by putting into an area where the other person can download.

midi's and a lot of the file produced by the various notation programs are quite easily sent by e-mail.