answer:You should use UTF-8. I believe it is more widely supported in email clients. As for the last question, the history of the development of text encodings, their redundancy, overlap, inefficiencies and features is impressively complex—including technical debates as well as politics. For Japanese, you should check out “CJKV Information Processing” by Ken Lunde. It’s the definitive resource in print (in English) for Chinese, Japanese, Korean and Vietnamese encoding, typesetting technology and information processing.