Topic Last Modified: 2006-02-28

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine whether the Exchange Installable File System (ExIFS or IFS) drive letter mapping is enabled:


If the Exchange Server Analyzer finds the DriveLetter registry value configured with a drive letter (such as M), an error is displayed.

Exchange 2000 Server introduced a feature named IFS. IFS is a kernel-level driver that surfaces some of the data in the Exchange information stores to the Microsoft Windows® file system. On new Exchange 2000 Server installations and on upgrades to Exchange 2000 Server from Exchange Server 5.5, IFS is automatically installed and a drive letter (by default, drive M) was assigned and mapped to the information store. This was performed using the \\.\BackOfficeStorage\ namespace.

Exchange Server 2003 supports IFS, but has the drive letter mapping disabled by default. The DriveLetter registry value is not present in new installations of Exchange Server 2003, and in an upgrade from Exchange 2000 Server to Exchange Server 2003, the registry value data, and therefore the drive letter mapping, is removed.

As a best practice, it is recommended that you do not enable the IFS drive letter mapping in Exchange Server 2003 and that you remove it in Exchange 2000 Server. There are known problems that can occur if the driver letter mapped to the IFS is accessed or scanned by anti-virus or file system-based applications. As a result, it is recommended that the drive letter mapping be removed if the IFS feature is not being used.

This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To correct this error

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to:


  3. In the right pane, double-click the DriveLetter value.

  4. In the Value data field, delete the listed letter so that the Value data field is blank.

  5. Close the registry editor and restart the Microsoft Exchange System Attendant service and the World Wide Web Publishing service for the change to take effect. When then System Attendant service is restarted, all services that depend on the System Attendant service, including the Microsoft Exchange MTA Stacks and the Microsoft Exchange Information Store services, will also be restarted.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (

For more information about removing the drive M mapping in Exchange 2000 Server, see the Knowledge Base article 305145, "How to remove the IFS mapping for Drive M in Exchange 2000 Server" (

For more information about adding the drive M mapping in Exchange Server 2003, see the Knowledge Base article 821836, "Drive M Mapping to IFS Is Not Present by Default in Exchange Server 2003" (