How do I disable the M drive mapping that the Exchange Installable File System (ExIFS) creates?
ExIFS creates a drive mapping that exposes the contents of the Exchange mailbox store. By default, this mapping is created on every Exchange 2000 Server machine, but the M drive isn't explicitly shared unless an administrator shares it. Having this mapping is useful in many circumstances. For example, I know of a large Exchange site that has disabled standard Windows 2000 file sharing and given each user a 300MB mailbox quota—users share files by putting them in a subfolder under their Inbox.
However, the M drive isn't completely safe. For example, you shouldn't back it up or scan it with file-based virus scanners. If users start adjusting permissions, bad things can happen (e.g, calendar problems, lack of access to messages and attachments, damage to the Exchange database). The Microsoft article "XADM: Do Not Back Up or Scan Exchange 2000 Drive M" (http://support.microsoft.com/support/ kb/articles/q298/9/24.asp) gives more information. To prevent these kinds of problems, Microsoft lets you prevent Exchange from creating the mapping. To prevent the mapping, modify the value of the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EXIFS\Parameters\DriveLetter registry subkey, where DriveLetter is the drive you don't want mapped. Usually, the subkey contains the string M; by clearing the value (but not deleting the key!), you can hide the ExIFS pseudodrive. After making this change, you have to restart the server. If you're using Outlook Web Access (OWA), you also must remap the two virtual servers that point to M:\something (e.g., M:\mbx—the public and Exchange virtual root directories under Default Web Site in the Internet Services Manager—ISM) so that they point to \\.\BackOfficeStorage\yourDomain\something (e.g., \\.\BackOfficeStorage\robichaux.net\mbx) instead.