Here is something out of Exchange tester's toolbox:
Before testing or using GB18030, you must configure your client and server as below for correct display of GB18030 characters.
Client machine
Set the system locale to Chinese
1) Go to Control Panels -> Regional and Language Settings -> Languages and make sure support for East Asian fonts is checked
2) Go to the advanced tab and make sure that the language is set to "Chinese (PRC)"
Download and install the GB18030 patch from
http://www.microsoft.com/downloads/release.asp?releaseid=32385
Change the font and language of acceptance options in IE to support GB18030
1) Run IE 6.0; navigate to Tools and then Internet Options to open the "Internet Options" dialog.
2) Click the Languages button to open the "Languages" dialog box
3) Click the Add button to open the "Add Languages" dialog box
4) Find and Add the language named "Chinese (China) [zh-cn]"
5) Click the Ok button until you are back to the "Internet Options" dialog box
6) Click Fonts button to open "Fonts" dialog.
7) Change the "Language Script" to Chinese Simplified
8) Select SimSun-18030 for both "Web page font" and "Plain text font".
Change the encoding options in IE to display GB18030 characters
1) From IE, navigate to View->Encoding and check that Chinese Simplified (GB18030) is the current encoding option. This may have to be done every time a file with GB content is opened from within IE.
Server
Download and install the GB18030 patch from http://www.microsoft.com/downloads/release.asp?releaseid=32385 . Please note here that if the Global Catalog Server is running Windows 2000, you need to install the patch on it too.
Set the following regkeys to 1: UseGB18030 and UseRegionalCharset
1) Open regedit
2) Expand HKEY_LOCAL_MACHINE->SYSTEM->CurrentControlSet->Services->MSExchangeWeb->OWA
3) On the right pane, right click and go New->Dword Value
4) Type UseGB18030 press enter
5) Click on the key to set the value to 1
6) Click on the UseRegionalCharSet key and make sure the value is set to 1
Outlook
To send a message encoded in GB18030
1) Within Outlook, go to Tools-> Options -> Mail Format and click on the button titled "International Options".
2) Change the drop down box titled "Preferred Encoding for Outgoing Messages" to "Chinese Simplified (GB18030)"
3) Make sure the checkbox titled "Auto-Select encoding for outgoing messages" is unchecked
OWA
To send a GB18030 message with OWA
1) Log in to OWA and open a new message window
2) Right click on the gray area of the window and from the drop down menu make sure that GB18030 encoding is selected
3) Copy and paste GB content in to the message body
4) Highlight the content and change the font to SimSun18030
5) Send the message
You Had Me at EHLO.