The M drive is merely a manifestation [1] of mail messages.
You can read quite a bit more on Windows Installable File System drivers on MSDN. A file system is really just a collection of APIs that allow you to navigate a set of data in a logical fashion - containers (folders) and items (files). It shouldn't be too hard to see how one might view mail data as containers (folders) and items (messages) [3].
So, the ExIFS driver, which is installed with Exchange 2000 is the "Exchange Installable File System driver." It allows a certain set of well known APIs [2] to view the containers and items. It just so happens that if you give a file system supporting those APIs a drive letter, you can see it through Explorer or a CMD window, or any of the other standard Windows file dialog boxes...because they use the file system APIs to access data. It's no different than a network drive or a RAM drive or a flash memory card or a zip drive or ... It is merely a manifestation of data in the form of folders and files. The thing to remember is that since it is just a view of the mail messages presented by the file system APIs, it's not necessarily the most feature rich way to manipulate that data. The manipulation via the ExIFS (M: drive) is limited by the set of file system APIs [2]. On the other hand, the ability to manipulate the data through a mail client like Outlook has a very rich set of APIs for dealing with mail data - much beyond the simple functions for finding and displaying files. The messaging APIs that are native to the Exchange store allow things like getrecipients, addattachment, resolvenames, etc.
So, the M: drive can be seen as an (abbreviated) acronym for "Merely a Marginally Manipulatable Manifestation of Mail Messages."
- To make evident or certain by showing or displaying.
- readfile, writefile, movefile, deletefile, renamefile, openfile, closefile, findfile, etc.
- It's slightly more complex than this because a mail message is actually a container as well. it contains a header and a body and perhaps one or more attachments, which themselves can be messages (containers). It also can contain multiple bodies (e.g mime multipart alternative content) that display based on the best capabilities of the client.
