XADM: MTA Does Not Deliver Messages with High Directory Service Activity (159184)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

You may have difficulty delivering messages with the Microsoft Exchange Server message transfer agent (MTA). The symptoms for this problem are as follows:

The directory service is consistently very busy (processor use is 20 percent or greater).
MTA processor usage is quite low.
The MTA work queue consistently has a backlog of messages.
Messages are not delivered to the server.
The global address list is very large (20,000 users or more).

RESOLUTION

Apply the fix mentioned in the "Status" section of this article. If this fix does not correct the problem, perform one of the following steps:

Create the Allow fuzzy proxy search registry value and set it to 2. To do this, you need to edit the 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. Start Registry Editor (Regedt32.exe).
2. Under the HKEY_LOCAL_MACHINE subtree, go to the following subkey:
  SYSTEM\CurrentControlSet\Services\MSExchangeMTA\Parameters
3. Define the following registry value:
  Allow fuzzy proxy search
  Set this value to 2. This case-sensitive registry value is a DWORD value type. If you set the Allow fuzzy proxy search value to 2, you disable the fuzzy proxy search. If this registry value does not exist, the MTA assumes that this setting has a value of 1, and enables fuzzy proxy searches.
4. Quit Registry Editor.
If the problem persists, disable the alternate recipient Redirect and Deliver option for every mailbox on the server. To do this, in each mailbox, click the Delivery Options tab, and under Alternate Recipient, click None.

STATUS

Microsoft has confirmed that this is a problem in Microsoft Exchange Server,version 4.0. This problem was corrected in the latest Microsoft Exchange 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

MORE INFORMATION

This behavior may occur if the MTA attempts to deliver a message addressed to an X.400 proxy that does not exactly match an address in the global address list, and the proxy contains a substring that is similar to other addresses in the global address list. For example, message delivery may be slow if a message is addressed to an X.400 proxy that is similar to the following:

X400:C=US;A= ;P=Microsoft;CN=PaulBon

This address does not fully match the defined X.400 address for that mailbox. The MTA makes a request for the DS to resolve the address if there are thousands of other X.400 proxies in the global address list that contain the following substring:

X400:C=US;A= ;P=Microsoft

If the directory service is unable to resolve the full address by means of an exact match, the directory service attempts to perform a fuzzy proxy search based on the parsed substrings.

By default, the MTA attempts to perform a fuzzy proxy search if it is unable to match the O/R address when it performs a DS_Search. To disable the fuzzy proxy search, add the Allow fuzzy proxy search registry value and set it to 2.

For additional information about the fuzzy proxy search in Microsoft Exchange Server versions 5.0 and 5.5, click the article number below to view the article in the Microsoft Knowledge Base:

176046 XCON: Routing Issues with Microsoft Exchange Server, Version 5.0