The Installable File System, or IFS, was a feature introduced in Exchange 2000 to allow access to the Exchange information store through Windows's file system APIs. The entire folder structure of the Exchange information store can show up as a mapped drive with subfolders, and each message or item represented as a file. A script written by an administrator or a third-party program could make easy use of the Exchange information store this way.
When Exchange 2000 is first installed, Exchange maps a drive to the Exchange information store through IFS. Normally drive M: is used for this, with three main subfolders: MBX (for user mailboxes), PUBLIC FOLDERS and PRIVATE FOLDERS. Note that the access control lists enforced on Exchange objects is maintained for their IFS counterparts.
Exchange 2003 also includes IFS support for the Exchange store, but unlike Exchange 2000, it is not mapped by default to a drive letter when Exchange is installed. This is done to prevent possible conflicts with existing drive letters, to prevent any exploitable security problems that might arise from having the information store mapped to a drive immediately -- and to prevent possible data corruption issues that might arise from, for instance, running an antivirus program on the IFS store. (To that end, don't attempt to run antivirus or backup solutions on the IFS store.)
To manually re-enable the drive M mapping for Exchange 2003, edit the Registry key HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesEXIFSParameters and add a new String value with the name DriveLetter and the value M. (If you choose a different value, then the drive letter will be set appropriately.) Note that if you remove or add the drive letter by changing or removing the DriveLetter value, the entire server will need to be rebooted to resynchronize.
Exchange 2003 does create mappings in IIS 6.0 for the Web Storage System:
\\.\BackOfficeStorage
\\.\BackOfficeStorage\<domainname>\MBX
\\.\BackOfficeStorage\<domainname>\Public Folders
\\.\BackOfficeStorage\<domainname>\Private Folders
These settings should not be changed if Outlook Web Access is in use.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter.
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