The Outlook search feature is limited to searching within 64 nested subfolders when you use Outlook 2010 in Cached Exchange mode. This behavior is by design.
This limitation does not apply to when you use Outlook in Online mode or to when slow search is used (that is, when Windows Desktop Search is disabled or not installed). This limitation is also not present when Outlook is started in safe mode.
This 64-folder limit can be reached when you use the Advanced Find
entry point and then click to enable the Search Subfolders
check box (Screen shot for this step is listed below).
Additionally, you can also reach this limit when you click the All Subfolders
button on the Search
ribbon tab (Screen shot for this step is listed below).Note
Search Folders in the Outlook Navigation Pane are not affected by this limitation.
After the search finishes, sort the results by folder. You can safely ignore the folders that are not subfolders of your target folder.
Run Outlook as administrator to prevent Outlook from accessing the Windows Desktop Search (WDS) index. Outlook then falls back to using slow search.
Set the PreventIndexingOutlook policy that is documented in the following Microsoft TechNet web site:
You should take Exchange search performance into consideration.
Disable indexing of the store type by policy. This is documented on the following Microsoft MSDN web site:
Narrow the search scope to specific subfolders.
If no other workarounds are possible, change the folder structure.