Vista Mail vs. Outlook Express: Page 3

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Database Architecture

At its core, Windows Mail runs with a completely different architecture than Outlook Express. Outlook Express presented a set of direct database files to both the user and the OS. At least four default folders are created with each “identity” in Outlook Express. These are:

C:Documents and SettingsLocal SettingsApplication DataIdentities{GUID}MicrosoftOutlook ExpressFolders.dbx

C:Documents and SettingsLocal SettingsApplication DataIdentities{GUID}MicrosoftOutlook ExpressOutbox.dbx

C:Documents and SettingsLocal SettingsApplication DataIdentities{GUID}MicrosoftOutlook ExpressInbox.dbx

C:Documents and SettingsLocal SettingsApplication DataIdentities{GUID}MicrosoftOutlook ExpressOffline.dbx

Outlook Express utilizes the single database file, Folders.dbx, as the master index for the entire messaging store. It holds the tree structure for all mail folders, the newsgroups on each news account, and even the options for the synchronization of “subscribed” folders. It is ultimately in this design that Outlook Express begins to fall short of many hopes and expectations. All mail items reside within each of these folders, meaning that the corruption of any of the folders results in the loss or corruption of all the mail stored within. Even worse, there are functional capacity limits for each of the individual files. If any of these files gets too large, typically near 2 GB, searching for mail and even opening Outlook Express becomes slow or even impossible.

For these reasons, the Windows Mail design team did away with the single storage-file design. Instead, Windows Mail utilizes a JET database, the same database engine in use for Exchange and Active Directory, and the very same instance in use in the Vista OS on which Windows Mail is installed. The database file tree structure that existed in Outlook Express now exists only as folders within the OS. All of these folders, as well as the pointers to the actual messages, are located in a single folder for each user.

The Windows Mail Folder Structure

If you were paying attention, you may have noticed our use of the term pointers regarding messages. Via JET, Windows Mail now stores each piece of mail and each news post as a separate file within the OS. Mail files are given the .eml file extension and news posts receive an .nws file extension. Each of these files is composed of two streams. For messages, the primary stream of the file is the RFC standard MIME. This is the portion of the message that is easily read by opening an .eml file in Notepad.exe.

An E-Mail File Opened in Notepad

The secondary stream is actually XML. Because JET is part of Vista and Vista supports even more metadata in the file’s file system than earlier OSes, this stream is populated with flags, account information, state information, and filter handlers that get promoted up into JET for categorization. This allows for the integration of the new Windows Search, which we’ll cover more in the section “Instant Search,” later in this chapter.

The utilization of the JET database on the OS provides myriad benefits. The most noticeable is easily the improvement in performance. Searching for mail, opening mail, and ultimately running the application is markedly faster due to the flatness of the file structure within the OS. A flatter file structure means it’s easier to grab data from the application level. In Vista, e-mail messages and news posts are found and displayed even as the user is typing criteria into the search engine, eliminating the extra actions of initiating a search and then perusing the search results for the appropriate mail content as opposed to only the filename. The use of JET also provides a self-cleaning mechanism from within the OS. As files are added and deleted, garbage collection processes within the OS groom the disk and ultimately the database in a very natural way that is transparent to the user and even the application. The result is a lighter application, a faster data store for mail, and a simpler organization of files and folders.


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