XCLN: Changing Parent Distinguished Name Lists Causes Corrupted Offline Address Books

Outlook 98 for Microsoft Windows NT or Outlook 2000 for Microsoft Windows NT users who use the offline Address Book may not be able to send an e-mail message to a user in the offline Address Book. After the user sends the e-mail message, the user may receive non-delivery report (NDR) error messages that are similar to the following: This issue occurs when users perform incremental offline Address Book downloads rather than full offline Address Book downloads.

This issue can occur if the parent distinguished name (PDN) list changes on the server.

To resolve this problem:

1. Obtain the latest service pack for Exchange Server 5.5.
2. For Outlook 2000 clients, obtain SP 2 for Office 2000.NOTE: For Outlook 98 clients, contact Microsoft Product Support Services to obtain a fix. Visit the following Microsoft Web site at:
   http://support.microsoft.com/default.aspx

   (http://support.microsoft.com/default.aspx)

To resolve this problem, obtain the latest service pack for Exchange Server 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
The English version of this fix should have the following file attributes or later:

Component: Outlook 98


Component: Outlook 2000

To work around this issue, perform a full offline Address Book download.

Microsoft has confirmed that this is a problem in Microsoft Outlook 98 and Microsoft Outlook 2000. This problem was first corrected in Exchange Server 5.5 Service Pack 4.

There is an architectural limitation in the offline Address Book differential download mechanism. This section describes how the offline Address Book works and how this limitation is manifested.

On the server, the Exchange Server system attendant creates an offline Address Book and places that offline Address Book in a public folder. To do this, the system attendant calls the Oabgen.dll file. This file contains all of the functions to create and update an offline Address Book. On the server, the offline Address Book is completely contained in an e-mail message as attachments. This e-mail message is placed in a public folder so that all clients can retrieve this e-mail message. To create the offline Address Book, the Oabgen.dll file scans all the entries in the global address list and builds the list from the global address list. In the offline Address Book, a PDN block is created that has all of the container names that have e-mail objects in the global address list. The following is an example of a PDN: An offline Address Book also contains relative distinguished names (RDNs). This is the user's directory name in the Exchange Server Administrator program. The following is an example of an RDN: The offline Address Book organizes a user by joining the RDN with the PDN, so that the user is actually the following: To put the two pieces together, there are pointers in the records that indicate that the address Test User is composed of the RDN at offset x, which is /cn=TestUser, and the PDN at offset y, which contains /o=Organization/ou=Site/cn=Recipients.

When an offline Address Book generation is run, two messages are created in a public folder: a message that contains a full download and a message that contains the changes after the last full download message was created. If there are new containers in the global address list after the last full download message was created, the PDN block is updated alphabetically with the new entry, and the new RDN to the changes message is included. When this new RDN is added to the changes message, a pointer to the PDN block offset is included.

If a user requests a differential download at this point, Outlook locates the changes message, and incorporates the changes into the current offline Address Book that is on the client. It is at this point that the limitation of the offline Address Book is manifested. Because the client only retrieves the changes message, and not the full download message, the client has an out of date PDN block. The PDN block that the client now has may not have a PDN for the new RDNs that were just merged, or if a container was removed, the PDN on the client still may contain that container.

If a new user was just merged, the user's offline Address Book may point to a PDN block that does not exist. This incorrect pointer can cause NDRs if the user tries to send a message to that user. The only way to make the user's PDN block match the server's PDN block is to perform a full download. The full download uses the full download message from the public folder, and therefore obtains the correct PDN list. This enables future differential downloads to work with the updated PDN block. This offline Address Book works correctly until the container structure changes.

Offline Address Book corruption can appear somewhat random because the PDN block is sorted alphabetically. If an entry is added to the PDN block, old pointers in the user's offline Address Book point to a totally incorrect place in the PDN block. Similarly, if an entry is removed from the PDN list, the pointers are incorrect.

What the Fix Does

Microsoft has developed a resolution for the preceding issue. In this fix, both the server and the client have been modified. This section describes how this fix addresses this issue.

On the Server

On the server, the Oabgen.dll file has been modified so that if the PDN list must be modified, the Oabgen.dll file does not post a changes message. This choice leverages behavior that the client exhibits if the changes message is absent, which is explained in the following section.

On the Client

On the client, the Emsabp32.dll file has been modified to locate one of the following registry keys: NOTE: The HKEY_CURRENT_USER value overrides the HKEY_LOCAL_MACHINE value if both values are present.

If either of the preceding registry keys are enabled, a user requests a differential download, and the client cannot find the changes message in the public folder, a dialog box is displayed that contains the following text: The user can click Yes or No in this dialog box. If the user clicks No, nothing is downloaded, and the user can continue to use the current offline Address Book. This behavior is necessary to ensure that if users are connected over a slow link, those users can stop a full download from occurring. This way, a user can schedule a full download when a full download is convenient.
If the Emsabp32.dll file does not find the registry keys, or the registry values are set to zero, Outlook reverts to the default behavior of the Emsabp32.dll file, which downloads the full offline Address Book if the changes message is not found. Also, there is no indication to the user that a full download is in progress. In some cases, a full offline Address Book download can take several hours.

If the user clicks Yes in the dialog box, a full offline Address Book is downloaded. This keeps the user's PDN list up to date with the server's PDN list.