Windows Live Mail XP API - integration framework for Windows Live Mail XP, also known as Windows Live Mail 2009.
The framework allows writing Windows Live Mail plugins using Visual C++, C#, VB and VB.Net, Delphi. This version allows customizing Windows Live Mail XP toolbar, accessing accounts, message folders, emails, Windows Live Mail contacts. Live Mail API works directly with DirectUI to allow user interface modifications, adding new buttons, images, etc.
The plugin development framework supports Windows Live Mail XP. If you interesting in Windows Live Mail for Windows 7 take a look on Windows Live Mail 2011 page.
To get started read Quick HOWTO or browse Windows Live Mail API online documentation.