Microsoft KB Archive/205533

= XCON: Exchange Server Message Transfer Agent in Large Site May Run Out of Entity Control Blocks =

Article ID: 205533

Article Last Modified on 10/28/2006

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APPLIES TO


 * Microsoft Exchange Server 4.0 Standard Edition
 * Microsoft Exchange Server 5.0 Standard Edition

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This article was previously published under Q205533



SYMPTOMS
If you install an Exchange Server computer in a large site, when the server attempts to send an e-mail message over an installed connector, such as the Internet Mail Connector in Exchange Server 4.0 or the Internet Mail Service in Exchange Server 5.0, the server may run low on or run out of Entity Control Blocks (ECBs).

The following events may be logged in the Microsoft Windows NT application event log:

Event ID: 248

Source: MSExchangeMTA

An internal MTA error occurred. An attempt has been made to process too many entity control blocks (ECBs) by a single thread. Number of ECBs processed: 10. [MTA DISP:ROUTER 14:331] (14)

Event ID: 41

Source: MSExchangeMTA

There are too many concurrently connected entities. There are no free entity control blocks (ECBs) available. There are currently %1 ECBs configured. [MTA DISP:ROUTER 12 119] (14)

Message delivery may also be slow.



CAUSE
An Entity Control Block is a segment of code that is created for each message transfer agent (MTA) and connector that a given MTA communicates with. The ECBs are created during MTA startup.

By default, the Exchange Server MTA is configured for 25 ECB connections to 25 other Exchange Server computers in a given site. This issue can occur if this server count is exceeded.



WORKAROUND
To work around this issue, run Performance Optimizer and change the Number of users setting to the number of users that the connector services, rather than the number of users on the local server. Also set the server to be a Multiserver and Connector server.

If this issue still occurs after you run Performance Optimizer, make the following registry changes:

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.

 Start Registry Editor (Regedt32.exe). Locate the Concurrent connections to LAN-MTAs value under the following key in the registry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeMTA\Parameters

 The default value is 40 in decimal format; change the value to 80. On the Edit menu, click DWORD, type 80, and then click OK. Locate the LAN-MTAs value under the same key in the registry. The default value is 20 in decimal format; change the value to 40. On the Edit menu, click DWORD, type 40, and then click OK. Locate the Number of Remote Sites Connected over LAN value under the same key in the registry.</li> The default value is 25 in decimal format; change the value to 50. On the Edit menu, click DWORD, type 50, and then click OK.</li> Locate the X.400 gateways value under the same key in the registry.</li> The default value is 20 in decimal format; change the value to 40. On the Edit menu, click DWORD, type 40, and then click OK.</li> Quit Registry Editor, and then restart the MTA.</li></ol>

Additional query words: 248 41

Keywords: kbprb KB205533

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