This event indicates that the Mail Submission Assistant (MSExchangeMailSubmission.exe) cannot handle the number of submission requests that are being made to the Exchange databases. This issue may occur if the mailbox server is under a heavy load. In this scenario, outbound messages may queue on the server.

The Assistants Infrastructure is part of the hosting application installation on servers that host the Mailbox server role. The Assistants Infrastructure is the component in Microsoft Exchange Server 2010 that separates message processing business logic from the information store. The separation of business logic from the store has the advantage of reducing the load on the store and makes it easier to implement changes in business logic design and testing. This business logic includes the following features:

• E-mail retention
  
  
• Resource scheduling
  
  
• Automated out-of-office messages
  
  
• Automated calendaring features
  
  

To handle business logic processing, the Assistants Infrastructure makes use of event-based and time-based assistants known as Mailbox Assistants. To handle mail submission requests from the mailbox to the bridgehead, the Assistants Infrastructure uses an assistant known as the Mail Submission Assistant.

To resolve this problem, do one or more of the following:

• Review the Application log and System log on your Exchange 2010 servers for related events. For example, events that occur immediately before and after this event may provide more information about the root cause of this error.
  
  
• To review detailed information about the cause of this alert, use the Operations Console in Operations Manager. For more information, see the "Introduction" section in this topic.
  
  
• Examine the event log entries for every Assistants Infrastructure and for each corresponding assistant.
  
  
• Collect performance information for all the Assistants Infrastructure counters by using the MSExchange Assistants object. Also, collect performance data for the particular Mail Submission Assistant object.There is one instance for every hosting application per database on the server. The instance name contains the service name of the hosting application's service together with the database name. Additionally, there is a total instance for each hosting application. The "total" captures consolidated values for each counter for all assistants that are hosted by the application.
  
  

Note:
If the Mailbox server hosts a public folder database, there will be a single instance for the database. This is because the Mail Submission Assistant must handle mail flow on any mail-enabled public folders in the database.

• Use the Exchange Troubleshooting Resolution Assistant (ExTRA) to obtain Event Tracing for Windows (ETW) traces. For more information, see the Scotch's Blog article, Another M e thod of Obtaining ExTRA Traces.
  
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• Move some users to other mailbox servers.
  
  
• Increase the number of Assistants Infrastructure threads for use with event-based assistant processing and time-based assistant processing. By default, the thread count for event-based processing is 12 per processor, and the default value for time-based processing is 16 threads per processor. To change the number of threads, create the following registry entries:
  
  HKLM\System\CurrentControlSet\Services\MSExchangeMailboxAssistants\ParametersValue name: EventDatabaseThrottleValue type: REG_DWORD
  
  Value data: 12 (default)Value name: TimeBasedDriverManagerThrottleValue type: REG_DWORDValue data: 16 (default)
  
  
• Resolve your issue by using self-support options, assisted support options, and other resources. You can access these resources from the Exchange Server Solutions Center. From this page, click Self-Support Options in the navigation pane to use self-help options. Self-help options include searching the Microsoft Knowledge Base, posting a question at the Exchange Server forums, and others. Alternatively, in the navigation pane, you can click Assisted Support Options to contact a Microsoft support professional. Because your organization may have a specific procedure for directly contacting Microsoft Technical Support, be sure to review your organization's guidelines first.
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.