Following through with its previous plans, Microsoft has released the specifications for its Outlook PST data format. The company announced in October that it was working with industry experts to prepare the technical documentation. Said documentation was made available for download a few days ago. You can read the 200-plus-page PDF, or download a 102MB zip file with 35 total PDFs covering formats like DOC, DOCX, and XLS.
PST files are used to contain several types of data, including email, calendar, and contacts in Outlook Personal Folders. Microsoft's decision to open the format comes in the interest of supporting interoperability. It wants vendors and customers to be able to access the data in PST files on a variety of platforms, so developers can read, create, and interoperate the information stored within them.