If you're intending to target People's Republic of China, you MUST (by Chinese law) support GB18030.
We are talking about email.
GB18030 support is currently only mandated for operating systems, and not currently for end-user applications (also embedded systems and PDAs are currently exempt).
I am not aware of *any* Chinese-language email being delivered using GB18030. Nor do I think that it is likely that GB18030 will ever be commonly used for email. Also note that GB18030 requires 4 octets for Unicode codepoints outside of GBK.
And I think it's worth noting that many (perhaps most) people in Asia are not happy with Unicode (including UTF-8!) because of the "Han unification" effect.
There's a great deal of FUD spread in Asia about Unicode, mostly traceable to a single individual. The "font problem" is greatly exaggerated. It *is* desirable to display a *language* in an appropriate font for that language; however the cost of using a "generic" font turns out to be greatly exaggerated.
Note that the correct differential is language, not "original character set".
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
