Many of my friends are having big problems in using Chinese in email because Yahoo, Hotmail and Yahoo are using different default encoding for the email subjects and contents.

Yahoo and Hotmail's default enconding is Western (ISO-8859-1) encoding;
Gmail's default encoding is Unicode (utf-8).

Case 1: When a message is sent from Yahoo in its default Western encoding with Chinese contents, Gmail can automatically convert it to Unicode and display the content correctly, Hotmail can just directly display the Chinese content in Western encoding correctly too.
But we found problem when the message is replyed in Gmail, Yahoo Mail/HotMail cannot display its unicode message correctly by default Western encoding.

Solution for Yahoo Mail/HotMail user: Go to View, then Character Encoding and select Unicode (UTF-8), then the Unicode message Gmail can be displayed correctly.

Case 2:When Yahoo/Hotmail users send Chinese Simplified(GB2312) message (by selecting that encoding before you type in the content) to Gmail user, the message cannot be displayed correctly in Gmail's Unicode environment. There is no way to read it correctly in Gmail.
Solution/Work around: Forward the message to your own Yahoo or HotMail account and use GB2312 encoding to display the message.

A general solution to avoid all this problem: save the whole message in Word or PDF format or even in graphic gif/jpg format and attach it in the email.

Still have questions? Any suggestions and comments are welcome.