From 4Team Corporation:
A free tool to archive Outlook data automatically even if Microsoft Outlook is closed. Split Microsoft Outlook data to multiple PST files. Split PST files according to selected criteria and filters using PST Splitter Pro Edition. Select if you wish to move or copy Outlook data.
The PST Splitter Free version gives you the same result as the Microsoft Outlook AutoArchive feature. The difference is - using AutoArchive, Outlook must be open in order to run the archiving process. Using PST Splitter files will be archived according to a schedule regardless of whether Outlook is running or closed.
Split the PST file into smaller Outlook data files and move them to separate Archive files. Reduce the size of your PST file, avoid reaching 2GB limitation and increase Outlook performance.
For more advanced PST splitting, use PST Splitter Pro Edition. It enables you to split Outlook data manually by various criteria, such as size, folders and accounts.