You may experience performance problems when you browse an LDAP server in Outlook

If you use Microsoft Office Outlook 2007 or Microsoft Office Outlook 2003 to browse a Lightweight Directory Access Protocol (LDAP) server, you may experience performance problems (slowdowns) while you view and search address lists.

This problem occurs when the directories of the LDAP server have more than 5,000 entries.

To work around this problem, follow these steps to disable LDAP address-list-browsing functionality in the Microsoft Windows registry.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following key in the registry if you use Outlook 2007:
   HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook
   Locate and then click the following key in the registry if you use Outlook 2003:
   HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook
3. On the Edit menu, point to New, and then click Key.
4. Type LDAP, and then press ENTER.
5. Click LDAP. On the Edit menu, point to New, and then click DWORD Value.
6. Type DisableVLVBrowsing, and then press ENTER.
7. On the Edit menu, click Modify.
8. Type 1, and then click OK.

You can also disable the LDAP address-list-browsing functionality in Group Policy.

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section of this article.

Outlook can create an address list that you can use to browse an LDAP server address list. This browsing feature set permits you to see a list of addresses when you open the address book, click anywhere in the address list, and then type a single character to move down the address list to the entries that start with that letter. For Outlook to provide this functionality for an LDAP server address list, the LDAP server must support either the Virtual List View (VLV) extension or a combination of two LDAP controls (the paged results and the server-side sort controls).

If your LDAP server does not provide either of these functionalities, you do not have the browsing feature set in Outlook. Particularly for the VLV extension, permission is not typically granted on the LDAP server for anonymous users to access the extension. Therefore, without a change in the permission assignments, the browsing feature set in Outlook is not available.

If the browsing feature set is not available in Outlook, you can still perform searches and select addresses from the LDAP server. However, you cannot see the pre-populated address book, and you cannot type a single character to move down the address list to the entries that start with that letter. In this non-browsing scenario, directories that have more than 3,000 entries are not affected by any adverse performance.

If you are using the browsing feature set in Outlook, directories that have more than 3,000 entries cause performance slowdowns that are not acceptable for everyday use. For example, if you have a directory of 5,000 entries, there may be a delay of 45 seconds between the time that you select the address book and the time that the browse list appears. Likewise, when you type the letter "t" to move to the entries that start with that letter, there is another delay of 30 seconds. Performance speed decreases in proportion to the number of entries that are in the directory.

If you have other clients that do perform well with the VLV extension, and you want to turn off the browsing feature set at the client level in Outlook, follow the steps in the "Workaround" section of this article to disable the browsing feature set.