Mar 26, 2009 05:50 AM|Nai-Dong Jin - MSFT|LINK
The Outlook 2007 has provided more object models to let the programmer to customize. Since there are new object models that does not exist in Outlook 2003. The 2007 AddIn or automation application cannot work with Outlook
2003. If you want to write an application work with multiple versions of Office. You need to develop against the lowest version which can be used with latter version.
In this case, develop against Outlook 2003 object model and use it with Outlook 2003/2007. More detailed information, please see