This article applies to the following:
6.x Email Manager for Outlook
Colligo recommends between 500 to 700 nodes within the PST, regardless of how they are stacked, for the best product performance. Generally, our testing reflected that deeper hierarchies produced better performance.
Possible ways to work with document libraries that have more than this number of folders is to add favorites to specific folders, or use the move and copy buttons in the Outlook ribbon and select Other SharePoint Location.