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How mailbox rules and Windows Desktop Search affect Outlook 2007

If you can't find what's slowing Outlook 2007 performance, check out two commonly overlooked causes -- excessive mail rules and Windows Desktop Search.

Two often overlooked causes of Microsoft Outlook 2007 performance problems are excessive mailbox rules and Windows Desktop Search. Exchange Server expert Brien Posey helps you determine if either of these two are to blame.

Excessive mailbox rules

Microsoft Outlook 2007 enables the creation of multiple mailbox rules. Because rules don't take up much space, you can create rules until they consume 64 KB (methods exist for extending that space to 256 KB).

What many power users don't realize is that each time a new message arrives, all of those rules need to be processed. Processing all of those rules consumes system resources and can adversely affect system performance. This is especially true if a user receives a high volume of mail and has a complex set of rules.

It's usually a bad idea to store an excessive number of items in a user's inbox. Having too many rules that process messages and move them to various folders automatically can also hinder performance. This is especially true if you create rules that move messages out of the default store.

For example, when Outlook is operating in cached Exchange mode, messages are stored in the Exchange inbox and a copy is written to an .ost file. If you create rules that move inbound messages to subfolders, Outlook will spend time and resources processing those rules when new messages arrive.

You won't notice a big performance hit unless you have an excessive number of rules. If you have rules that move messages out of the inbox and into a folder in a .pst file, then a performance hit may be more noticeable because Outlook has to manipulate multiple data files.

Windows Desktop Search

Windows Desktop Search indexes a PC's contents so that the user can quickly search for specific items. It indexes .pst files and .ost files, among other things.

Windows Desktop Search doesn't normally cause too many Outlook performance problems. Outlook is most heavily affected when a new user profile is created on a PC.

For example, suppose that you order a new computer. When it arrives, you install the standard desktop image that everyone in your company uses. The first time that you log into the new computer, Windows will create a profile for you.

The first time that you open your mailbox in Outlook, a couple of different things happen. First, your mailbox data is copied from the Exchange server to an .ost file on the computer's local hard drive. Second, Windows begins indexing mailbox content.

Indexing.pst files and .ost files can take a while to complete and may slow performance, but that will return to normal when indexing is done.

The indexing process will also slow down when system resource usage exceeds a certain point. This means that Windows will index .pst files and .ost files most efficiently when the computer is idle, so you might want to allow the initial indexing process to run overnight.

To confirm Outlook's indexing status, choose the Instant Search -> Indexing Status options from the Tools menu. Outlook will display a dialog box that shows how many items have been indexed and how many items still need to be indexed.

The indexing process communicates directly with Exchange Server instead of indexing data stored locally, so it can be an inefficient process. Having users operate Outlook in online mode can also help to improve performance.

About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at

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