The Interoperability team at Microsoft announced that it will open up the pst-file format specifications to the public under the Open Specification Promise (OSP) license. This means that other developers would be free to use the pst-file format in their solutions and read/write to it without any restrictions. Currently it requires Outlook to be installed and using the Messaging API (MAPI) or the Outlook Object Model (OOM).
The documentation is still in the early development stages and the final version of the documentation is expected to be released in the first half of 2010.
More information about this can be found at the blog of of the Interoperability Team and at the blog of the Outlook Team.
