Article ID: 870926
Article Last Modified on 10/25/2007
APPLIES TO
- Microsoft Exchange Server 2003 Enterprise Edition
- Microsoft Exchange Server 2003 Standard Edition
- Microsoft Office Outlook 2003
Important This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
SUMMARY
This article describes how Outlook 2003 Cached Exchange Mode works in a Microsoft Exchange Server 2003 environment. Cached Exchange Mode is a new feature in Microsoft Office Outlook 2003. When Cached Exchange Mode is enabled, Outlook 2003 uses a local copy of your mailbox. At the same time, Outlook 2003 maintains an online connection to a remote copy of your mailbox in Exchange Server.
INTRODUCTION
Cached Exchange Mode is a new feature in Outlook 2003. When you turn on Cached Exchange Mode in Outlook 2003, and when the connection from your computer that is running Outlook 2003 to the Exchange Server 2003 computer is not available, Outlook switches to the Trying to connect state or to the Disconnected state. If the connection is restored, Outlook switches to the Connected state or to the Connected (Headers) state. Any changes that you made while you were offline are synchronized automatically when a connection to a server is available. You can continue to work while changes are synchronized.
Outlook 2003 Cached Exchange Mode offers you the following benefits:
- After messages have been cached locally, typical user operations do not cause interactions that block the server. Quickflagging, marking a message as read, replying, and editing require a small amount of data to be pushed up to the server to keep the mailboxes synchronized. However, the pushing of data occurs in the background. This behavior causes much faster access to messages and to attachments, because you work from the local copy instead of the server copy.
- Additionally, Cached Exchange Mode causes no loss of conventional functionality. New e-mail notifications, full Global Address List details, free/busy lookup, public folder access, and delegate support function as expected. However, this is true only when a network connection to an Exchange Server computer is present.
- Cached Exchange Mode provides intelligent use of bandwidth. This functionality is enabled by synchronizing only headers on slow connections (connections that are slower than 128 kilobits per second [Kbps]). This functionality works only when a network connection is present.
Additionally, Cached Exchange Mode offers administrators the following benefits:
- Reduced server load. After messages are cached locally, re-opening the same message does not require server transactions.
- Reduced network load. After messages have been pulled over the network one time, subsequent access to those messages does not cause additional network traffic. Because messages are also compressed, there is an additional reduction on network load.
MORE INFORMATION
How to enable Cached Exchange Mode in Outlook 2003
By default, Cached Exchange Mode is enabled when you install Outlook 2003 for the first time. However, when you upgrade to Outlook 2003 from an earlier version of Outlook, Cached Exchange Mode may not be enabled. During the upgrade process, the systems administrator can enable or disable Cached Exchange Mode.
To enable Cached Exchange Mode in Outlook 2003, follow these steps:
- On the Tools menu, click 'E-mail Accounts'.
- In the E-mail Accounts dialog box, click View or change existing e-mail accounts, and then click Next.
- Make sure that Microsoft Exchange Server is selected, and then click Change.
- In the E-Mail Accounts dialog box, click to select the Use Cached Exchange Mode check box, and then click Next.
- Click OK, and then restart Outlook 2003.
How Outlook 2003 synchronizes data in Cached Exchange Mode
The time that is required to complete the initial synchronization between Outlook 2003 and Exchange Server 2003 depends primarily on the size of the mailbox and on the speed of the connection to the Exchange Server 2003 computer.
Access to all data is not available until the initial synchronization is complete. Therefore, we recommend that you use a fast connection when you start Cached Exchange Mode for the first time.
After the initial synchronization is complete, Outlook 2003 keeps the local copy up to date automatically. If a change is made to the data on the server, Outlook 2003 is notified to synchronize the changes. Changes on the server may occur if a new message was received, or if another client made a change to existing data. If changes are made to the local data, Outlook 2003 synchronizes those changes with the server automatically. This process occurs in real time and does not require user intervention.
Cached Exchange Mode synchronization timing
To provide a good balance between usability and network efficiency, the timing of synchronization communications between Outlook 2003 and Exchange Server 2003 has been optimized by using synchronization timers.
Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
You can change these synchronization timer values by creating and by modifying the following registry keys and values under the HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\Cached Mode registry key:
- Upload=dword:0000000f (default is 15 seconds).
- Download=dword:0000001e (default is 30 seconds)
- Maximum=dword:0000003c (default is 60 seconds)
By default, whenever the client is in Cached Exchange Mode and a user makes a local change, the Upload timer starts. Changes have the following effects:
- If a local change occurs during the 15-second window of the Upload timer, the Upload timer restarts.
- If no other local changes before the 15-second window expires, the data is synchronized to the server.
- If changes continue to occur before the 15-second window expires, all changes are synchronized to the Exchange Server computer after one minute. There is no additional delay.
When the Exchange Server computer notifies Outlook 2003 of a change, the Download timer starts. Outlook delays receiving the change information. This behavior reduces server load and improves network performance, because Outlook is frequently notified of multiple server changes in quick succession. All notifications that occur in the 30-second window of the Download timer are grouped together, and then they are processed at the end of the timer. The timer is then reset to wait for the next server notification. When a new mail notification is received, Outlook 2003 synchronizes folders where new or changed items reside. Unread counts are updated, and then any rules are processed.
Order of folder synchronization in Outlook 2003
When Outlook 2003 synchronizes with an Exchange Server 2003 computer, Outlook 2003 uses an intelligent learning algorithm that is transparent to you. This algorithm puts higher synchronization priority on the folders that you use most frequently. This behavior gives you an optimal user experience. Outlook 2003 synchronizes folders in the following order (until you have been using Outlook long enough to train a synchronization priority):
- Utility folders (common views, views, and security settings)
- Calendar
- Contacts
- Drafts
- Inbox
- All other folders (defined by the user)
- Sent Items
- Deleted Items
- Public Folder Favorites (added by the user)
Outlook 2003 Sync Issues folder
Outlook 2003 will skip and log any bad items or malformed items on the server, and then Outlook 2003 continues to synchronize correctly. Bad items are put in the appropriate Server Failures folder or in the appropriate Local Failures folder in the Sync Issues folder. The Sync Issues folder and its sibling folders are visible only in the Folder List view of the Navigation pane. They do not appear in the All Mail Folders list in the Mail section of the Navigation pane.
Practices to avoid when you use Outlook 2003 with Cached Exchange Mode
Because Outlook 2003 has several ways to connect to Exchange Server 2003, some functions and features of Outlook 2003 do not work well with Cached Exchange Mode. The following sections describe practices to avoid. Avoiding these practices helps you achieve the most efficient overall performance when you use Outlook 2003 with Cached Exchange Mode.
Common Outlook 2003 features that reduce the effectiveness of Cached Exchange Mode
Some Outlook 2003 features reduce the effectiveness of Cached Exchange Mode because they require network access or because they bypass Cached Exchange Mode functionality. The primary benefit of using Cached Exchange Mode is that it shields the client from network issues and from server connection issues. When you are not using Cached Exchange Mode, features that rely on network access may cause delays in Outlook 2003.
The following Outlook 2003 operations rely on network access. Therefore, these operations may cause delays in client performance when the connection to Exchange Server 2003 is slow:
- Accessing of e-mail by delegates
- Opening another user's calendar or folder
- Using a public folder that has not been cached
Certain Outlook 2003 operations such as looking up free/busy information also require network access to retrieve the required information. This requirement may cause a delayed response even when users have fast connections to Exchange Server 2003 data. The delays may occur unpredictably instead of occurring only when the feature is accessed.
When Cached Exchange Mode is deployed, consider disabling or not implementing the following features:
- The combination of the alert feature and the digital signatures on e-mail messages. To verify a digital signature, Outlook 2003 must verify the digital signature with a network server. By default, Outlook 2003 displays an alert message that contains a part of an e-mail message when new e-mail messages arrive in your Inbox. If you click the alert message to open a signed e-mail message, Outlook 2003 uses network access to look for a valid signature on the e-mail message.
- Multiple Address Book containers. Typically, the Address Book contains the Global Address List and the Contacts folders. Some organizations configure subsets of the Global Address List. These subset address books are displayed in the Address Book. These subset address books can also be included in the list that defines the search order for address books. If subset address books are included in the search order list, Outlook 2003 may require access to the network to check these address books every time that a name in an e-mail message is resolved.
Note Do not include custom properties on the General tab of a Properties dialog box in the Global Address List. Outlook must retrieve the custom properties online. If the custom properties are displayed, the user experience of opening the Global Address List details can be compromised. Additionally, clicking the Organization tab or other tabs will also require network access.
Outlook 2003 add-ins
Installing particular Outlook 2003 add-ins may offset the benefits of using Cached Exchange Mode. Some add-ins bypass the expected functionality of headers mode (Download Headers Only) in Cached Exchange Mode by accessing Outlook 2003 data with the object model. For example, when you use Microsoft ActiveSync to synchronize a handheld computer, full Outlook 2003 items are downloaded instead of only headers. This behavior occurs even over a slow connection. Additionally, the update process will be slower than if the items are downloaded in Outlook 2003, because some programs may use a less efficient synchronization method.
Client-side rules
When you use Outlook 2003 with Microsoft Exchange Server 2003, you can use both server-based and client-side rules. Server-based rules can be processed on the server. For example, a user who uses the mailbox for the delivery location might have a rule that deletes all e-mail messages from a specific alias. Because both the Inbox and the Deleted Items folder are stored on the server, the rule can be processed there without interaction from the client. Client-side rules require some processing by the client.
For example, a user has a personal folder (.pst) file where e-mail messages of certain types are stored. The .pst file uses a rule that moves all e-mail messages from a specific alias to that folder. In this case, the server cannot perform all the processing because the .pst file is located on the local computer and can be accessed only by Outlook 2003 and not by Exchange Server. Exchange Server 2003 creates a deferred action item on the server that runs the next time that files are synchronized. Because users must run deferred actions, client-side rules may have a very big effect on system performance, particularly when they work over slower connections. To promote better system performance, consider doing the following:
- Remove any unnecessary client-side rules.
- Click the Stop processing more rules option in the Rules Wizard.
- Do not use the junk-mail rule. The junk-mail rule may slow down the synchronization process.
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