Performance data from SMTP Categorizer Queue Length counter

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2005-11-18

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 Categorizer Queue Length performance counter of the SMTP Server performance object to analyze performance data. The Exchange Server Analyzer reports the total number of messages found in the Categorizer queue.

The SMTP Server\Categorizer Queue Length counter indicates the number of messages in the Simple Mail Transfer Protocol (SMTP) Categorizer queue waiting for directory service attribute searches using global catalog servers. As a general guideline, the maximum value should be less than 10.

By default, the Exchange Server Analyzer retrieves a sample every 30 seconds for a two-hour period. The Exchange Server Analyzer reports the maximum value for the performance counter during the collection interval. The Exchange Server Analyzer also reports the value that is at the ninetieth percentile of all collected values.


If you list in ascending order all the values that the Exchange Server Analyzer collected, the ninetieth percentile is the value at the ninetieth percent position in the list. The ninetieth percentile value indicates the high values of this counter during the collection interval.

In some instances, the maximum value will be the value at a peak point in the interval. Therefore the maximum value is not representative of the whole interval. The median value does not always accurately indicate load because the median value includes idle time during the collection interval. Therefore, the Exchange Server Analyzer reports the maximum value and the ninetieth percentile value.

The Categorizer Queue Length counter indicates the number of messages in the message categorizer queue. The categorizer performs the following core operations:

  • It resolves and validates all recipients.

  • It determines limits and restrictions for all recipients.

  • It expands distribution lists if necessary.

  • It determines whether the message is for local or remote delivery

An increase in the Categorizer Queue Length counter indicates that there could be potential problems with server performance issues, Directory Service Access (DSAccess), the Active Directory® directory service, or outages with key servers in the Exchange Server organization. An increase in the Categorizer Queue Length counter would indicate slowness or no responsiveness in consulting Active Directory or in handing messages off for local delivery or SMTP.

The information in this baseline message is for information purposes only. There is no action required.

For more information about suggested thresholds of performance counters, see Troubleshooting Exchange Server 2003 Performance (