XCON: Delivery Restrictions Max CPU and Slow Down Msg Delivery

• Microsoft Exchange Server, versions 4.0 and 5.0

SYMPTOMS

During an extended period of time the following behavior might be seen on an affected Microsoft Exchange Server computer:

Performance monitor counters

• MTA Work Queue: 2000.
• Messages/Sec: 0,1.
• Message Bytes/Sec: 500.
• Directory Lookups/sec: 30.
• The MTAs and DS combined CPU is nearly 100%.
• Looking at the MTA queues using the Microsoft Exchange Server Administrative program does not show any items in the queues.
• The MTADATA contains more than 2000 DB*.DAT files.
• Message delivery is very slow.

CAUSE

Access to a connector such as the Internet Mail Connector (IMC), located on the affected server, is limited using distribution lists (DLs). Due to this restriction, transferred messages have to be checked against this access limitation and the DLs have to be expanded. Depending on the size and the nesting level of the DLs, this may cause a considerable performance degradation.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Exchange versions 4.0 and 5.0. This problem was corrected in the latest Microsoft Exchange Server 4.0 and 5.0 U.S. Service Packs. 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

WORKAROUND

• Do not restrict access to connectors such as the IMC.
• Do not use DLs to restrict access to connectors such as the IMC.
• Increase the memory and/or number of processors on the affected computer.
• Introduce a separate computer and operate the connector in question from there.

MORE INFORMATION

Using DLs to restrict access to connectors is very CPU intensive, even though a dedicated HUB Server might be used to operate connectors from. As a result, the faster the computer and the more memory it has, the faster it will be able to process mail. Even after applying the fix, Microsoft strongly suggests that you consider adding more memory and/or processors to the computer in question. Together with the fix described in this article a new registry value is introduced

   DL Member Cache Size <REG_DWORD>

   H_KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
      \MSExchangeMTA\Parameters

Installation

1. Stop the MSExchangeMTA service.

2. Stop the MSExchangeIMC service.

3. Backup the following files from the <path>\exchsrvr\bin directory by renaming them or copying them to another location:

         Emsmta.exe
         Mtacheck.exe
         Mmiext.dll
         Saalog.dll
         Ems_rid.dll
         P2.xv2
         Address.dll
   

4. Backup the following file from the \<Path>\Exchsrvr\Mtadata directory by renaming it or copying it to another location:

         P2.xv2
   

5. Backup the following file from the \<Path>\Exchsrvr\Connect\Msexcimc\Bin directory by renaming it, or copying it to another location:

         Address.dll
   

6. Copy Emsmta.exe, Mtacheck.exe, Mmiext.dll, Saalog.dll, Ems_rid.dll, P2.xv2, and Address.dll to the \<Path>\Exchsrvr\Bin directory.

7. Copy P2.xv2 to the \<Path>\Exchsrvr\Mtadata directory.

8. Copy Address.dll to the \<Path>\Exchsrvr\Exchsrvr\Connect\Msexcimc\Bin directory.

9. Restart the MSExchangeMTA, MSExchangeIMC, and any additional service possibly stopped in steps 1 and 2.