Topic Last Modified: 2010-02-16

The Microsoft Exchange Server 2010 Management Pack for System Center Operations Manager includes a performance data collection engine that is used to query performance counter objects on computers running Exchange 2010. For this Operations Manager rule, data is collected by using the performance counter specified in the Details table.

To review the value of the performance counter that generated this alert, in Operations Manager, double-click this alert, and then click the General tab. Review the description of the alert that includes the variables specific to your environment.


Product Name


Product Version

14.0 (Exchange 2010)

Object Name

MSExchangeTransport Queues

Counter Name

Unreachable Queue Length

Instance Name


Sample Interval


Server Role

Ex14. Edge Transport

Critical Error Threshold


Rule Path

Microsoft Exchange Server/Exchange 2010/Edge Transport/Transport Queues

Rule Name

Unreachable Queue Length - sustained for 5 minutes - Red(>250) - Edge Transport.


The Unreachable Queue Length performance counter measures the number of messages currently in the unreachable queue. This alert indicates that the unreachable queue length has been greater than 250 for five minutes.

The categorizer sends messages to the unreachable queue when there is no known route to their destinations. Typically, an unreachable destination is caused by a configuration error that affects the delivery path. For example, the messages will be sent to the unreachable queue if the following conditions are true:

  • There are messages in the "" remote delivery queue.

  • You delete the Send connector that is used to reach the domain.

By default, the messages in the unreachable queue have the status of Ready. Messages in the unreachable queue are never automatically resubmitted. Messages remain in the unreachable queue until they are manually resubmitted by an administrator, removed by an administrator, or the value specified in the MessageExpirationTimeOut parameter passes.

For more information about the unreachable queue, see Understanding Transport Queues.

User Action

To resolve this alert, do the following:

  • If the messages are in the unreachable queue due to a temporary issue, you can try resubmitting the messages in the unreachable message queue. You can do this by using Exchange Queue Viewer or by running the Resume-Message cmdlet in the Exchange Management Shell. For more information, see Resubmit Messages in Queues.

  • Inspect the messages in the unreachable queue to identify the reasons why the messages are unreachable. For more information about reasons why messages may be put in the unreachable queue, see the "Scenarios where messages are put in the unreachable queue" section in Message Rerouting and the Unreachable Queue.

For more information about Queue Viewer, see Using Queue Viewer.

For more information about using the Shell to manage queues, see Using the Exchange Management Shell to Manage Queues.

For More Information

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.