Back in February, Microsoft released public specifications for PST files, the databases used by Outlook for storing and archiving e-mail. To these specifications, Microsoft has now added a pair of developer-oriented open source projects: the PST Data Structure View Tool for cracking open PSTs to browse inside them, and the PST File Format SDK, a cross-platform C++ library for working with PST files programmatically.

The SDK project is not yet finished; presently it only provides read-only access to PST data, though write support is 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.

PST files represent a big hurdle for anyone wanting to switch away from Outlook. There are many millions of gigabytes of mail stored in PSTs, but no robust way to access them from anything that isn't Outlook. With many people unwilling to give up massive e-mail archives, they're left with no option but to stick with Microsoft's e-mail client.

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.