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Microsoft KB Archive/297019

From BetaArchive Wiki

Article ID: 297019

Article Last Modified on 5/15/2007


  • Microsoft Office Outlook 2007
  • Microsoft Office Outlook 2003
  • Microsoft Outlook 2002 Standard Edition
  • Microsoft Outlook 2000 Standard Edition
  • Microsoft Outlook 98 Standard Edition

This article was previously published under Q297019


This article tells you why personal folder files (.pst files) are unsupported over a local area network (LAN) or wide area network (WAN) link. The .pst files are not meant to be a long-term, continuous-use method of storing messages in an enterprise environment.

The article also suggests two alternatives to .pst files. You can use .ost files or Microsoft Windows Terminal Services.


The Microsoft Exchange Server 4.0 team created .pst files with the intent of letting a person maintain a copy of their messages on their local computer. The .pst files also serve the purpose of a message store for users who do not have access to a Microsoft Exchange Server computer (for example, Microsoft Outlook Internet Mail Only (IMO) mode users).

However, .pst files are not meant to be an enterprise network solution. Although it is possible to specify a network directory or a Universal Naming Convention (UNC) path as a storage location for a .pst file, network usage is not meant to be a long-term, continuous-use method of storing messages in an enterprise environment.

A .pst file is a file-access-driven method of message storage. File-access-driven means that the computer uses special file access commands that the operating system provides to read and write data to the file.

This is not efficient on WAN or LAN links because WAN/LAN links use network-access-driven methods, commands the operating system provides to send data to or receive from another networked computer. If there is a remote .pst (over a network link), Microsoft Outlook tries to use the file commands to read from the file or write to the file, but the operating system then has to send those commands over the network because the file is not on the local computer. This creates a great deal of overhead and increases the time it takes to read and write to the file. Additionally, the use a .pst file over a network connection may result in a corrupted .pst file if the connection degrades or fails.

For more information about issues that you may experience with the network storage devices or with servers that house shares, visit the following Web site:

Other Behaviors of .pst Files over WAN/LAN Links

  • All operations take longer.
  • Write operations can take approximately four times longer than read operations.
  • Outlook has slower performance than the Exchange Client.

For the reasons mentioned above, Offline Folders (.ost) files and personal address book (.pab) files on a network share that are accessed remotely are also unsupported configurations.

If there are roaming users in the organization, visit the following Microsoft Web site:


Microsoft recommends the following solutions, instead of .pst files over a LAN or WAN.

Exchange Server with .ost File

When you are working over a WAN or LAN, it is better to use the offline folder files (.ost files) to allow the remote client to work without being connected to the server. .ost files support local replication, which means that all folders and their data can be replicated to the .ost, not just e-mail messages, as is the case when you use remote mail. The use of .ost files is therefore more efficient and more useful. .ost files also do not have a dependency on the availability of the Exchange Server computer (except to synchronize new data from the server to the client and vice versa), because the information is cached in the local .ost file. This improves performance because the information being viewed is stored on the local drive while the master copy of the data remains on the server, where it can be accessed and backed up. .ost files also provide data redundancy, which ensures greater integrity and recoverability of the data.

Microsoft Terminal Services

If an enterprise wants to use Outlook over WAN or LAN links, it is highly efficient to run the Microsoft Windows Terminal Server service. With Terminal Services, only enough information required to update a display is transferred. The potential benefits in having many remote users based on Terminal Services, instead of using either .pst files or .ost files, would be significant in any network bandwidth conservation analysis.


For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

208480 Description of the purpose and capacity of Outlook storage facilities

177446 How to test Microsoft Remote Procedure Call performance

Additional query words: OL2K network share network drive OST supported OL3002 OL2007

Keywords: kbstore kbemail kbinfo KB297019