Topic Last Modified: 2006-09-06

The Microsoft® Exchange Server Analyzer Tool includes a performance data collection engine that is used to query performance counter objects on computers that are running Exchange 2000 Server or Exchange Server 2003. The performance data collection engine collects data from the Cat: Categorizations in progress and the Categorizer Queue length performance counters of the SMTP Server performance object to analyze performance data.

The Cat: Categorizations in progress performance counter shows the number of categorizations in progress whereas the Categorizer Queue length performance counter shows the number of messages in the categorizer queue.

For this query, the Exchange Server Analyzer retrieves a sample every 6 seconds for a two-minute period. The Exchange Server Analyzer reports the average value for the performance counter during the collection interval.

The Exchange Server Analyzer examines the average number of categorizations in progress and compares that number against the number of categorizations still in the queue.

The Exchange Server Analyzer displays an error if, over the sample period, the following conditions are true:

The categorizer performs the following core operations:

This error indicates that there are messages stuck in the categorizer queue that have failed categorization with a retryable error.

Generally, messages accumulate in queues because the advanced queuing engine is unable to categorize the message. The advanced queuing engine may be unable to access the global catalog servers and access recipient information. Alternatively, the global catalog servers may be unreachable or performing slowly. In addition, messages can accumulate for the following reasons:

You can examine the properties of the queue to determine the cause of the failure. For example, if the queue properties display a message that resembles "An SMTP error has occurred," you should review your server's event logs to locate any SMTP errors. If there are no events in the log, you should increase the SMTP logging level.

For more information about how to troubleshoot Exchange and SMTP queues, see the following Exchange resources:

The message categorizer performance counters are published separately for each SMTP virtual server instance. For a list of the available performance counters related to the Message Categorizer, see Microsoft Knowledge Base article 231734, "XCON: Performance Monitor Counters for Message Categorizer" (