Microsoft made open the format of Outlook databases

Microsoft has published the official specifications for the Outlook Personal Folders (PST) format. The Data Structure View Tool and File Format SDK utilities are also released to demonstrate the structure of the format and provide tools for writing and reading email databases without Outlook installed on the computer.

Opening format specifications may lead to its use on alternative operating systems. (In the comments suggest that this, rather, will lead to the emergence of converters to other formats.)