Microsoft KB Archive/282115

= If more than 4 Exchange EDK connectors are installed, mail flow stops =

Article ID: 282115

Article Last Modified on 10/28/2006

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APPLIES TO


 * Microsoft Exchange Server 5.5 Standard Edition

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This article was previously published under Q282115



Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SYMPTOMS
In Exchange Server 5.5 Service Pack 2 (SP2), with more than four EDK connectors of the same type installed on the same computer, mail flows fine. After you apply Exchange Server 5.5 Service Pack 3 (SP3), if more than four EDK Connectors are installed, mail stops processing on all EDK Connectors.



WORKAROUND
To work around this issue, increase the following threads in the registry. Customers have been able to run eight EDK Connectors on an Exchange Server 5.5 computer with SP3 (or later) installed by increasing these threads.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

Increase the threads in the following registry keys (unless otherwise stated, all of these keys are found in the HKLM\SYSTEM\CurrentControlSet\Services hive, and all values are in hexadecimal format):

'''..\MSExchangeIS\ParametersPrivate\Gateway In Threads=0x2

..\MSExchangeIS\ParametersPrivate\Gateway Out Threads=0x2

..\MSExchangeIS\ParametersSystem\Background Threads=0x60

..\MSExchangeIS\ParametersSystem\Max Threads (Public+Private)=0x64

..\MSExchangeMTA\Parameters\Concurrent XAPI sessions=0x32

..\MSExchangeMTA\Parameters\Concurrent connections to X.400 gateways=0x12'''



Gateway In Threads and Gateway Out Threads
These settings are the number of threads that the information store creates on behalf of an EDK Gateway when the gateway logs on to the information store. The Gateway In Threads value moves messages from the message transfer agent (MTA) to the information store's MTS-OUT queue (destined for the gateway). The Gateway Out Threads value moves messages (coming in from the gateway) out of the information store's MTS-IN queue to the MTA for distribution. Therefore, if you increase the Gateway In Threads value, you increase the pipe between the MTA and the information store for outbound Internet Mail Service messages.

Background Threads
This is the number of threads allocated to run background processes such as defragmentation of the stores. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

265186 MTA fanout slows on multiprocessor servers and messages back up in information store

Max Threads
Any time that you add a thread to a registry setting under any information store key, you must increase the Max Threads setting accordingly.

Concurrent XAPI sessions
Among other things, this value defines how many sessions can be open between the MTA and information store. By default, the Concurrent XAPI sessions value is set to 0x50. After you run the Exchange Server Performance Optimizer, the Concurrent XAPI sessions value may be set to 0x30. In this case, it is recommended that you set the registry value back to 0x50. To determine if the Concurrent XAPI sessions to the information store are being exhausted, add the following counter to a Performance Monitor chart:

Object 'MSExchangeMTA Connections'

Counter 'Associations'

Instances'Microsoft Private MDB'

If delivery from the EDK Connector is sluggish, you may need to further increase the Concurrent XAPI sessions value and increase the private and public information stores' send and delivery threads. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

265186 MTA fanout slows on multiprocessor servers and messages back up in information store

Concurrent connections to X.400 gateways
This value represents the maximum number of concurrent connections to remote X.400 MTAs. The default value for Concurrent connections to X.400 gateways is 0x6. If you treat the SXC Connector as an additional X.400 gateway and increase this value to 0x18, you can help improve the performance of the SXC Connector.

The settings that are making the difference here are actually the &quot;Max Threads (Public+Private)&quot; and &quot;Background Threads&quot;. There are fewer available threads in Exchange 5.5 SP2, SP3, and SP4 due to additional features like virus scanning which use some of the threads that were previously allocated or store processes right out of the box. Increasing the Gateway In and Gateway Out threads doesn’t help unless enough total threads have been allocated. This is where the Max and Background threads come into play. In order to get up to eight EDK connectors working, it is necessary to m0dify the registry settings to the values shown above.

For more information about information store threads, click the following article numbers to view the articles in the Microsoft Knowledge Base:

234065 Troubleshooting the MTA queue to the Internet Mail Service

166621 Gateway Out threads not set correctly by Perfwiz.exe

234702 MTA queue to information store processing slowly

257252 Default registry entries for Microsoft Exchange Server Information Store

For more information about MTA threads, click the following article numbers to view the articles in the Microsoft Knowledge Base:

247782 Mail transfer slow across connectors, event IDs 3120 and 9316 appear

234280 How to increase the ability of the MTA to pass mail over slow network connections

265186 MTA fanout slows on multiprocessor servers and messages back up in information store

Additional query words: IS IMS

Keywords: kbprb KB282115

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