SMTP server does not support X-LINK2STATE verb

[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: 2009-09-14

The Microsoft® Exchange Server Analyzer Tool initiates an SMTP session with the Exchange server to validate that the proper Exchange SMTP verbs are listed. If the X-LINK2STATE verb is not listed, a warning is displayed.

The X-LINK2STATE verb is used by Exchange to update the link state tables on the routing masters. The link state tables record up-to-date information about the status of the SMTP links throughout the Exchange organization. Exchange uses this information to pick the lowest cost and most reliable routes when routing messages. This functionality is also referred to as "Intelligent Routing."

The X-LINK2STATE verb is required by Exchange for efficient routing, and is not used by other SMTP providers. As such, the functionality is provided in a file (xlsasink.dll) that is installed and registered by Exchange Setup.

There are two known reasons why this warning may be returned. First, some administrators may have disabled xlsasink.dll as a way to work around the intelligent routing functionality it provides. This is not a recommended best practice and will likely lead to performance and reliability problems. In this case, it is recommended that you reinstall Exchange on the affected computer to install and register xlsasink.dll.

Secondly, this warning may be returned if you are running an antivirus product that installs and uses its own SMTP protocol stack to scan messages. In this case, the antivirus software may run its own SMTP stack that intercepts and scans messages before they reach the Exchange SMTP stack. In this case, the antivirus SMTP stack is not using X-LINK2STATE verb. It is recommended that you run the antivirus software in a mode that does not require it to install its own SMTP stack on the Exchange server.

For more information about X-LINK2STATE and other proprietary verbs used by Exchange, see the Microsoft Knowledge Base article 812455, "Definitions of Verbs That Are Used Between 2 Exchange Servers" (

For more information about how to view Exchange command verbs and reinstall Exchange Server 2003, see the Knowledge Base article 822939, "Messages That Are Sent in the Exchange Server 2003 Organization Are Not Delivered" (