Stephen Griffin announced the release of Outlook 2010 Messaging API (MAPI) Code Samples. Among the additions to MAPI for the next version of Microsoft's email client is “support for 64-bit Microsoft Outlook—Reference topics for applicable API elements have been updated to correspond to new header files that support 64-bit Outlook. These header files are now available as a download at Outlook 2010: MAPI Header Files. If your existing 32-bit MAPI application is going to be running on a 64-bit operating system with 64-bit Outlook installed, you will need to rebuild your 32-bit application as a 64-bit application, MSDN.
More info: Download (codeplex)