Event ID - 9646

Event Id9646
DescriptionClosing Mapi session "/o=First Organization/ou=First Administrative Group/cn=Recipients/cn=XY" because it exceeded the maximum of 250 objects of type "objtMessage".
Event InformationIn Exchange 2003 server, when you try to send more than 250 messages or 100 attachments by using a batch or script, the messages or attachments may not be sent, and events that are similar to this may be logged in the application event log.
CAUSE: This issue occurs because of a limit on the number of items that clients can open. By default, this limit is set to 100 for attachments and 250 for messages.
RESOLUTION: 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. To resolve this issue, follow these steps: On the Exchange 2003 computer, click Start, click Run, type regedit in the Open box, and then click OK. Locate and then click the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem On the Edit menu, point to New, and then click Key. Type MaxObjsPerMapiSession, and then press ENTER. For each object type that is listed in the event ID 9646 message (in the "Symptoms" section of this article, the example object types are objtMessage and objAttachment), follow these steps: On the Edit menu, point to New, and then click DWORD Value. Type the object name (for example, type objtMessage), and then press ENTER. Press ENTER again to open the Edit DWORD Value dialog box, type 500 in the Value data box, and then click OK. Close Registry Editor.
Reference Links Event ID 9646 is logged when you try to send many messages in Exchange Server 2003

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