Starting with WDS 3.01, to be able to use Windows Desktop Search to index an outlook profile running in online mode requires that you use group policy to enable this functionality. We index cached mode profiles by default, but online mode crawling is a large performance hit on the server causing the Slow Findrow rate for Mailbox Stores to soar. This has always been an issue with the default behavior, but it is nice to see that we now disable this by default for Online mode profiles.
More information on this can had from the WDS Administration guide. Here is a snippet from this guide.
Using WDS and Microsoft Outlook\Exchange
Finding items in e-mail has been a concern for business people for many years. The hard part is finding a way to keep a current index of all e-mail messages and attachments without excessively taxing the mail server. WDS supports Outlook indexing in both cached and uncached mode. However, WDS 3.01 must be configured via Group Policy to index e-mail when cached mode is turned off (Note, this is different from WDS 2.6x which indexed online content by default).
The two group policy settings that are used to enable/disable this functionality and to force cached mode outlook profiles is the following:
This has also been updated in the Windows 2008 online documentation at http://technet2.microsoft.com/windowsserver2008/en/library/584732fa-ad15-4cc6-9c1b-469add7da5621033.mspx?mfr=true