One of the many discussions that come up often over the years while onsite has to deal with the concern of PST files that are saved throughout the network. Microsoft future direction with the product is to try to de-emphasize the usage of the PST as we see in the archive mailbox feature in Exchange 2010.
Not only are they hard to back up, but they also can lead to discovery issues, potential data loss if they become corrupt, or harder to get to the necessary data via mobile devices or OWA for instance. One of the biggest things is that PSTs are not supported on a file server while Outlook has these files opened which has been the case for many years. This unsupported scenario is mentioned below:
Personal folder files are unsupported over a LAN or over a WAN link
Also, this configuration can cause severe windows kernel resource depletion because of how NTFS handles PST files. The windows performance team wrote a very interesting blog that goes over this very big risk:
Network Stored PST files … don’t do it!
One way it is possible is to restrict the creation or further use of PSTs. There are registry entries that you can deploy via group policy that prevent users growing the current size of PSTs all the way to no PSTs at all. For more information about this please see the following:
A network administrator can add the DisablePST registry value to a registry key so that all the users of a computer cannot create or access Outlook .pst files in Outlook 2003
How to configure the size limit for both (.pst) and (.ost) files in Outlook 2007 and in Outlook 2003