what's your original encoding? ANSI or Unicode?

you'll also need to know the language used in the e-mail, is't only simplified or mixed with some traditional chinese, I also noticed some people writing Chinese using Japanese shift-JIS (I can differentiate Chinese and Japanese, the two language structure are different!)

try decode one-by-one using all chinese, japanese, and korean to test which one appeared correctly

note: you posted in wrong category, you should put in 'IT' or 'computer' and not 'wordplay'