Forecast: Drizzle

To the Outlook team in Redmond, Washington, "drizzle" means more than just that region's frequent weather occurrence. Drizzle is the new Exchange Server synchronization concept that Microsoft plans to incorporate into the next version of Outlook. Drizzle is one of several architectural and connectivity changes that the company says will improve Outlook's performance, especially for users who aren't continuously connected to the server.

Although not as ambitious as the Local Information Store, which Microsoft had planned for Outlook 2002 and later removed from the product, this new "cached" mode for Outlook will offer many of the same features. Outlook will store mailbox and public folder data locally but connect to the Exchange Server on demand to get free or busy status information and to access Active Directory (AD). Also, users will be able to switch between online and offline operation without restarting Outlook.

The drizzle connection mode will improve replication to local offline folder files by synchronizing headers before item bodies and by providing multiple background threads to download more messages simultaneously. Users can also control the size of items that replicate to the local cache. Microsoft expects synchronization times to remain about the same because the same amount of data will flow between server and client, but the company hopes that these changes will improve efficiency for users as they read the updates in their Inboxes, especially over remote connections.

Supporting drizzle connections will require changes for both the Exchange Messaging API (MAPI) provider and the format of the offline folders (OST) file. Both OST files and Personal Folders (PST) files in the next version of Outlook will support up to 33TBs of data, significantly exceeding the current 2GB size limit. A registry key will control the maximum file size. Outlook will log changes to PST files with a timestamp, making it theoretically possible to perform incremental backup and synchronization (although Microsoft has no current plans to include either feature with the product). Because of these changes, OST and PST files you use with the next version of Outlook won't be compatible with past versions.

Another significant architectural change that Microsoft will include with the next Outlook version is support for MAPI over HTTP, a feature that will encrypt remote procedure call (RPC) packets inside HTTP requests to provide a secure connection to Exchange over the Internet, without the need for a VPN connection. Updates on the back end will handle the necessary authentication at both the firewall and the Exchange server.

The client experience will also change. Microsoft plans to completely overhaul the Outlook UI, paying special attention to accessibility components to bring the software into more complete compliance with Americans with Disabilities Act (ADA) guidelines. Outlook now has many functions that work only with the mouse, not the keyboard (e.g., the Outlook Bar and access to attachments), so the UI updates will be welcome.

Microsoft made it clear at last week's Microsoft Exchange Conference (MEC) in Orlando that Outlook will continue in its role as the premier Microsoft Exchange client. Although you can choose from a growing number of Microsoft messaging and collaboration tools—including Outlook Web Access (OWA), SharePoint Team Services, and SharePoint Portal Server—Outlook remains a powerful tool for centrally organizing and managing communications and information of all kinds.