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Microsoft KB Archive/925815

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Knowledge Base

An Exchange 2007 server stops responding to a MAPI client and logs event ID 9646 in the Application log

Article ID: 925815

Article Last Modified on 1/22/2007


  • Microsoft Exchange Server 2007 Enterprise Edition
  • Microsoft Exchange Server 2007 Standard Edition

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


A server that is running Microsoft Exchange Server 2007 stops responding to one or more MAPI clients. Additionally, an event that resembles the following is logged in the Application event log: Event ID: 9646
Type: Error
Source: MSExchangeIS
Closing Mapi session “/o=Exchange Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=user” exceeded the maximum of 500 objects of type “objtFolder”.

Note The description of this event may vary depending on the object type.


This problem may occur if a MAPI client opens more than the default value of the server objects that are included in the following table.

Note The default values of several server objects were increased in Microsoft Exchange Server 2003 Service Pack 1 (SP1) and in later versions of Microsoft Exchange. The increased values are shown in the "Value in Exchange 2003 SP1 and in later versions of Exchange" column.

Entry Default value Value in Exchange 2003 SP1 and in later versions of Exchange
objtMessage 250 250
objtFolder 500 500
objtAttachment 100 500
objtFolderView 500 500
objtMessageView 500 500
objtAttachView 250 500
objtStream 50 250
objtACLView 50 50
objtRulesView 50 50
objtFXSrcStrm 50 50
objtFXDstStrm 50 50
objtCStream 50 50
objtNotify 500,000 500,000


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.

In Exchange 2007, the number of server-side objects that are allowed to be opened by MAPI clients is limited. This behavior prevents a single MAPI client from exhausting resources on the Exchange server. When the event log error that is mentioned in the "Symptoms" section occurs, it indicates that a MAPI client may be opening too many objects or may be leaving too many objects open on the server. If the event log error occurs, investigate any third-party applications or add-ins that are running on the MAPI client.

Additionally, investigate the user behavior that is associated with the indicated logon. This will help you better understand why the default number of objects is insufficient. In rare circumstances, the number of resources is insufficient and may have to be adjusted. However, use caution before you adjust the maximum number of objects that are allowed. When you increase the maximum number of an object type, you also increase the memory that may be consumed by client requests. Incorrectly configuring this value could lead to out-of-memory warnings or virtual memory fragmentation warnings.

You can add a registry key that adjusts the maximum number of resources that a MAPI client can use at the same time. This adjustment overrides the default limit of each server object that is mentioned in the "Cause" section.

Note You should adjust only the value for the object type that is referred to in the event log error that is mentioned in the "Symptoms" section. You should adjust these values with caution. Additionally, only increase the value in small increments. For example, only increase the value by 100.

To add a registry key that limits the maximum number of resources that a MAPI client can use at the same time, follow these steps:

  1. Click Start, click Run, type regedit, and then click OK.
  2. Expand the following registry subkey:

    \\HKEY_LOCAL_MACHINE SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem

  3. Right-click ParametersSystem, point to New, and then click Key.
  4. Type MaxObjsPerMapiSession, and then press ENTER to name the new subkey.
  5. Right-click MaxObjsPerMapiSession, click New, and then click DWORD Value.
  6. Type Object_type, and then press ENTER to name the object.

    Note Object_type is the name of the object type in the event log error that is mentioned in the "Symptoms" section. For example, type objtMessage, and then press ENTER.
  7. Right-click Object_type, and then click Modify.
  8. In the Value data box, type the number of objects to which you want to limit this entry, and then click OK. For example, type 350 to increase the value for the objtMessage object. The default value is 250.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


For a complete list of Microsoft Product Support Services telephone numbers and for information about support costs, visit the following Microsoft Web site:

Additional query words: XADM

Keywords: kbeventlog kbclients kbtshoot KB925815