This goes back a while and I just plain forgot to post about it.
Back in February of 2010, Microsoft released a public specifications for PST files, the databases used by Outlook for storing and archiving e-mail. To these specifications, Microsoft also added a pair of developer-oriented open source projects:
- PST Data Structure View Tool for cracking open PSTs and browsing inside of them
- PST File Format SDK, a cross-platform C++ library for programmatically working with PST files.
Though the core Office document formats are now XML-based open standards, alleviating such lock-in issues, Outlook has continued to use a complex database format for storing mail, making interoperability difficult. With the documentation and these software projects, the days of being locked into Outlook could be coming to an end.
The SDK project is still not finished; seemingly it still only provides read-only access to PST data, though write support is purportedly planned. Both tools are released using under the Apache License 2.0. This means that they can be incorporated into proprietary, closed-source projects, as well as other open source projects.
Overall the information available at the Microsoft Interoperability site is very, very useful and I would strongly recommend a visit.