It took a while, but today the Exchange Team released the long awaited Microsoft Exchange PST Capture Tool (initial version 126.96.36.199). The tool can be used to discover and inject PST files in an Exchange 2010 Exchange Online mailbox or archive.
The tool was originally from Red Gate and known as PST Importer. It’s architecture consists of three components: the central service, (optional) agents for PST discovery, registration and collecting PST files and an administrative console (image by Red Gate):
The online documentation can be found here.
Note that although it’s only supported for Exchange 2010 and Exchange Online, you can use it with Exchange 2007; it’s only untested (and probably unsupported) with that product.