PST File
From mail2web.com Wiki
A .pst file (Personal Folder File) is the file format used by Microsoft Outlook. This is generally the format that is used to export multiple mail, calendar, contact and other items from Outlook to a single file. With our Business Exchange, mail2web Mobile Email and mail2web Mobile Email Pro services we fully support import and export of .pst files.
The Business Exchange Professional and mail2web Mobile Email Pro plans support full import/export via the Outlook 2003 and Outlook 2007 clients.
You can use the Import and Export options available in the Control Panel in the End-User Management area, or though the OWA in the My Email Settings section. Please note that the Import and Export .pst feature through the Control Panel only supports Outlook 97-2002 .pst format, which does not support Unicode.
See this article for details on importing your PST file.
