Back in October of last year, Microsoft announced plans to release the documentation for the PST file format – the file where your Outlook email, calendar, and contact data is stored on a PC. The documentation was to be released under Microsoft’s Open Specification format, said the blog post, which means that anyone could implement the .pst file format “on any platform and in any tool, without concerns about patents, and without the need to contact Microsoft in any way.”
Now that documentation has been made publicly available. On MSDN, anyone can read through all the details about the PST Structure Specification, including all the data structures it uses, examples, considerations, data algorithms, and product behavior.
Armed with this info, developers will be able to interoperate with PST data in both server and client scenarios on the platform of their choice. You can access the full spec details here: https://msdn.microsoft.com/en-us/library/ff387869.aspx.