An Exchange 2007 Server Stops Responding to a MAPI Client

Microsoft Exchange Server 2007 will reach end of support on April 11, 2017. To stay supported, you will need to upgrade. For more information, see Resources to help you upgrade your Office 2007 servers and clients.


Applies to: Exchange Server 2007, Exchange Server 2007 SP1

This topic provides information about how to troubleshoot a Microsoft Exchange Server 2007 server that stops responding to a MAPI client and generates an event log error with the following information:

Event ID: 9646

Type: Error

Source: MSExchangeIS

Description: Closing Mapi session "/o=Exchange Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=user" exceeded the maximum of 500 objects of type objtFolder.

This problem may occur if a MAPI client opens more than the maximum number of server objects. In Exchange 2007, the number of server-side objects that are allowed to be opened by a single MAPI session is limited. This behavior prevents a single MAPI client from exhausting resources on the Exchange server.

When an Exchange 2007 server stops responding to a MAPI client and generates Event 9646, it indicates that a MAPI client may be opening too many objects or may be leaving too many objects open on the server.

The following table lists the default values for the maximum number of server objects that can be opened at one time in Exchange 2007.

Default values of the maximum number of open server objects

Entry Default value




























To resolve the problem, do the following:

  • Investigate any third-party applications or add-ins that are running on the MAPI client. Some third-party applications keep objects open for long periods of time or open many objects concurrently.

  • 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 cases, you may need to add a registry key to adjust the maximum number of open objects. This new registry key will override the default value. Such rare cases include situations in which it is acceptable or necessary to use applications that keep objects open or open many objects concurrently.


    When you increase the maximum number of an object type, you also increase the memory that may be consumed by all client requests connecting to the server. Incorrectly configuring this value could lead to out-of-memory warnings or virtual memory fragmentation warnings.


    Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

Before You Begin

To perform the following procedure, the account you use must be delegated membership in the local Administrators group. For more information about permissions, delegating roles, and the rights that are required to administer Exchange 2007, see Permission Considerations.


To use Registry Editor to adjust the maximum number of open objects that a MAPI client can use at the same time

  1. Start Registry Editor (regedit).

  2. Locate 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 the object type, and then press ENTER to name the entry. For example, type objtMessage, and then press ENTER to create an entry that changes the default maximum of objtMessage objects.

  7. Right-click the entry that you created in Step 6, and then click Modify.

  8. In the Value data box, type the new maximum number of objects to which you want to limit this entry, and then click OK.


The server will automatically recognize the new limit within five minutes.