Categorizer queue length beyond threshold

[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: 2006-02-13

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.

If the Exchange Server Analyzer determines that the Categorizer Queue Length counter has exceeded the peak value of 10 during the sample time slice, the Exchange Server Analyzer displays an error.

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.

The categorizer performs the following core operations:

  • Resolves and validates all recipients.

  • Determines limits and restrictions for all recipients.

  • Expands distribution lists if that is required.

  • Determines whether the message is for local or remote delivery

This error indicates that there may be problems with server or network performance, 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 may indicate a either a slow response or no response in consulting Active Directory or in handing off messages for local delivery or SMTP. This might cause delayed mail delivery.

To address this error:

  • Verify that sufficient Active Directory resources are available to the Exchange server. This includes both domain controllers and global catalog servers. The recommended practice is to maintain a 4:1 ratio between Exchange server processors and global catalog server processors of similar speed.

  • From Exchange System Manager, verify that all domain controllers listed on the Exchange server’s DSAccess tab are functioning correctly. This includes servers listed in the ConfigDC, domain controller, and global catalog server roles.

  • Monitor network performance between the Exchange server and its chosen domain controllers and global catalog servers to determine whether there is a network performance bottleneck.

  • Monitor processor utilization on the Exchange server and also processor utilization of the Inetinfo.exe process. This includes the categorizer component.

  • Verify the health of Exchange-related user and group objects by using the e2kdsinteg configuration object from the ConfigDSInteg tool in Microsoft Exchange Server Deployment Tools ( Objects that have malformed addresses or incomplete information can cause delays in recipient determination and delay categorization.

For More Information

For more information about troubleshooting Exchange Server performance issues, see Troubleshooting Microsoft Exchange Server Performance (