Topic Last Modified: 2005-11-18

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 XEXCH50 verb is not listed, a warning is displayed.

Among other things, the XEXCH50 verb is used by Exchange for public folder replication. Running a version of SMTP on an Exchange server that does not support the XEXCH50 verb will break public folder replication.

The XEXCH50 verb is not used by other SMTP providers; therefore, the functionality is provided in a file (peexch50.dll) that is installed and registered by Exchange Setup.

The Exchange Server Analyzer may return this warning 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 uses its own SMTP stack to intercept and scan messages before they reach the Exchange SMTP stack. In this case, the SMTP stack in the antivirus software is not using the XEXCH50 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 or run such software at the incoming perimeter of your SMTP network. If you have disabled the SMTP stack for the antivirus software, and you still get this warning, reinstall Exchange to install and register peexch50.dll properly.

For more information about XEXCH50 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 2000 Server, see the Knowledge Base article 319885, "XCON: Messages Sent in the Exchange 2000 Server Organization Are Not Delivered" (

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" (