Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry key to determine whether the Lookup Sid Cache Expire registry entry is present:


The Exchange Server Analyzer displays a non-default configuration message if the following conditions exist:

On Exchange servers that are running Exchange 2000 Server Service Pack 3 or later, the information store creates a cache that contains Security Identifiers (SIDs) and indicates whether the SID is a user object or group object. This cache is created and populated when a public folder is first touched. After the cache is populated, all calls to look up account SIDs are first directed to the information store cache. If the SID is not in the information store cache, the call is made to the domain controller, and then the information for that SID is added to the cache.

By default, the cache is maintained for one hour. If the cache exceeds the default 8 kilobytes (KB) of entries, older cache entries are removed to make room for the new entries. You can use two registry keys to adjust both the default cache time (Lookup Sid Cache Expire) and the default cache size (Lookup Sid Cache Size). It is recommended that you do not change these default settings unless you have evidence that making this change will increase performance.

This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.
To revert to the default configuration
  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersPrivate

  3. In the right pane, locate and delete the Lookup Sid Cache Expire value. If the Lookup SID Cache Size value is also set, delete it, too.

  4. Exit the registry editor and restart the Microsoft Exchange Information Store service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows registry" (

For more information about the Lookup Sid Cache Expire registry value, see Microsoft Knowledge Base article 328907, "XADM: Access Control List Upgrades Cause Slow Public Folder Performance; Fix Requires Exchange 2000 SP2" (