Switching to or running Outlook in Online mode against an Exchange 2003 server may exhibit slower than normal performance when clicking on particular folders in your mailbox that contain high item counts.
This is a known issue when the “Show in Groups” option is turned on in Outlook when many items exist in a particular folder. The fix is actually two parts. One for the server side and one for the client side. Note: The server side fix is not necessary for Exchange 2007.
What you might see in Performance Monitor is similar to the load that Client side search engines add. This counter in particular is “Slow Findrow Rate” located under MSExchangeIS Mailbox. One might think that this counter is only used for detecting client search engines, but this counter increases whenever an application is crawling through a users mailbox.
In this case, Outlook creates a search restriction (“Show in Groups” with a descending date sort order) initially using a Fast FindRow call, but the server immediately switches to a Slow FindRow call which causes a large delay in returning the view for that newly created restriction while items in that particular folder are being queried. This could lead up to the dreaded RPC dialog box or the balloon stating the Outlook is requesting data from the server. While we are creating this restriction on the Exchange Server, this may also cause an added CPU performance hit. Since these restrictions are not cached, these problems may occur each time the user clicks on these folders that may have high item counts.
To better optimize this search restriction behavior, an optimized search was added server side so that these restrictions created by Outlook will use the Fast FindRow call method instead of switching to the Slow Findrow method. This provides a huge performance gain and mitigates the Outlook delay problems.
To be able to handle these optimized searches efficiently, your server performance has to be within our recommended performance guidelines, so even though you have applied these fixes, there is still a possibility that these problems could occur due to underlying performance problems server side.
Here are the links to the articles and fixes for each.
Exchange 2003 Server Side fix
Error message when you enable the "Show in Groups" option for a folder that contains thousands of e-mail messages in Outlook: "Outlook is retrieving data from the Microsoft Exchange Server <ServerName>"
Description of the Outlook 2003 hotfix package: February 21, 2008
Description of the Outlook 2007 hotfix package: February 27, 2008