Anyone who has ever dealt with Microsoft Outlook will know the .pst file format – it’s the binary, undocumented file in which all data from Outlook is stored – emails, contacts, calendar, you name it, it’s in there. Microsoft has announced that it will release detailed technical documentation on the Outlook .pst data format.
http://www.osnews.com/story/22394/Microsoft_To_Open_up_Outlook_pst_Format