XADM: MTA Fails to Deliver Messages with High DS Activity

• Microsoft Exchange Server, version 4.0

SYMPTOMS

You may have difficulty delivering messages with the Microsoft Exchange Message Transfer Agent (MTA). The symptoms for this problem are as follows:

• The Directory service (DS) is consistently very busy (processor usage is 20 percent or greater).
• MTA processor usage is quite low.
• The MTA WorkQueue consistently has a backlog of messages.
• Messages are not being delivered to the server.
• The GAL is very large (20,000 users or more).

CAUSE

This problem is caused by time-consuming fuzzy proxy Directory service (DS) searches on large Global Address Lists (GALs).

RESOLUTION

Apply the fix referenced below. If this does not correct the problem, do one of the following:

• Create the registry entry "Allow fuzzy proxy search" and set it to 0:

1. Start Registry Editor (Regedt32.exe).

2. Under the HKEY_LOCAL_MACHINE subtree, go to the following subkey:

         SYSTEM\CurrentControlSet\Services\MSExchangeMTA\Parameters
   

3. The registry value that needs to be defined is as follows:

         Allow fuzzy proxy search
   

   Set this value to 0. This case-sensitive registry value is a DWORD. Setting "Allow fuzzy proxy search"=0 disables the fuzzy proxy search. If this Registry value does not exist in the registry, the MTA will assume a value of 1 for this setting and thus fuzzy proxy searches are enabled.

4. Quit Registry Editor.

If the problem still persists, disable the alternate recipient "Redirect and Deliver" option for every mailbox on the server. To do this:

• Click the "Delivery Options" tab on each mailbox and set the Alternate Recipient option to "None."

STATUS

Microsoft has confirmed this to be 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 can occur when the MTA attempts to deliver a message addressed to an X.400 proxy that does not exactly match an address in the GAL, and when the proxy contains a substring similar to other addresses in the GAL. For example, message delivery may be slow if a message is addressed to an X.400 proxy similar to the following:

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

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

By default, the MTA attempts to perform a fuzzy proxy search if it is unable to match the O/R address when performing a DS_Search. The fuzzy proxy search can be disabled by adding the registry value "Allow fuzzy proxy search" and setting it to 0.