Getting the Most Out of the Microsoft Outlook Client : Using Cached Exchange Mode for Offline Functionality

3/14/2011 6:15:26 PM
Outlook 2007 continues to support Cached Exchange mode. Cached Exchange mode, or Cached mode for short, refers to a configuration where Outlook is storing the messages and calendar items locally. Unlike the old Personal folder file (PST) storage method, Cached mode utilizes an OST file. This file is synchronized with the Exchange server on a regular basis. This means that there are two copies of the mailbox at all times. One copy lives on the Exchange server and one copy lives on the Outlook client.

This configuration has many advantages in terms of performance and reliability. For example, imagine that a user is connecting to their Exchange server over a dial-up connection and isn’t running Cached mode. The user receives a message with a large attachment. The user sees the new message and opens the attachment. Now, the message has to be downloaded to the user’s computer. This takes several minutes because of the size of the file and the relatively slow link speed. This usually results in unhappy users because they had to wait several minutes between wanting to open the attachment and the attachment actually opening.

Now, let’s view this same scenario with Cached mode. In Cached mode, the attachment is downloaded in the background when the message arrives, assuming the Outlook client is attached to the server. The message with the attachment doesn’t appear in the mailbox until the contents have been downloaded and cached locally. Now, when the user sees the message appear in the Inbox, the files associated with the attachment are already on the local system. The user opens the attachment and it opens immediately. This results in a happier user.

The truth of the matter is that the download time of the message was exactly the same in both scenarios. However, the perceived difference is that the Cached mode situation was faster because the user doesn’t know when the message was sent. This situation also takes great advantage of the idle time of the user. Most messages arrive and are fully downloaded to the client while the user is away from their system or doing other things. This means that when the user is actively working with email, there aren’t any delays in moving data.

Because the data downloaded is only a mirror of the Exchange Server mailbox, the content available via OWA is exactly the same. Similarly, if the user were to get another computer or a new computer, Outlook simply creates another copy of the data locally to keep in sync.

With the OST file locally stored, the user is able to work with the contents of their mailbox even when not connected to the Exchange server. Changes made locally will sync back to the Exchange server. Like most replication performed by Microsoft, the newest copy always wins and overwrites older changes. This allows a traveling user to reply to messages, organize folders, and create calendar entries while away from the office. Upon connecting to the Exchange server, their local changes get applied to the Exchange server copy. This is really an optimal configuration for traveling users and users who have limited connectivity.

The User Experience in Cached Exchange Mode

When the user is connected to the Exchange server, the phrase “Connected to Microsoft Exchange” appears in the lower-right corner of the Outlook 2007 window. The message “All Folders Are Up to Date” should also be displayed when synchronization is up to date.

When connectivity is lost, the message says “Disconnected” and gives the date and time the offline folders were last updated.

When connectivity is first restored, the message says “Trying to Connect.” As connectivity is reestablished, the phrase “Connected to Microsoft Exchange” reappears, and to the left are updates informing the user what is automatically occurring to get the mailbox up to date.

These messages could be any of the following:

  • Waiting to Update the Full Items in Inbox

  • Sending Complete

  • All Folders Are Up-to-Date

The user might occasionally find that people appear to be missing from the Global Address List (GAL). While running in Cached mode, Outlook 2007 no longer gets its GAL from the global catalog. The client downloads the Offline Address Book. This is what allows the user to look up addresses while not connected to the network. The user can trigger a download of the OAB at any time. Important to realize is that, by default, Exchange Server only updates the OAB every 24 hours. As such, it’s possible for a user to be added to Exchange Server after the OAB generation has occurred. Users not running in Cached mode would see the new user in the GAL but the Cached mode users wouldn’t see them until the OAB was updated and they downloaded the latest copy.

Deploying Cached Exchange Mode

Cached mode can be deployed by using the Office Customization Tool or through enabling this option using domain Group Policy. Be aware that setting it via Group Policy on a large number of users drastically increases network traffic to the Exchange server. Outlook in Cached mode has to download the entire mailbox. Environments where mailbox size limits aren’t set are especially impacted by this. Imagine 200 users logon on Monday morning and a GPO sets their Outlook to Cached mode. If each user had 100MB of mail in their mailbox, there would be 20GB of data being copied from the Exchange server. This could be especially impacting if some of those users were coming across WAN connections to get to Exchange Server.

If possible, only set a user to Cached mode when they are on the same LAN of the Exchange server or when they are first created in Exchange Server. This reduces the traffic at the Exchange server.

Deploying Cached Exchange Mode Manually

When configuring a user’s Outlook profile manually, it’s possible to configure Cached mode at that time.

To configure Cached mode manually, do the following:

Begin configuring a user profile in the standard manner.

When the E-Mail Accounts page is reached, make sure the Use Cached Exchange Mode check box is checked.

Finish configuring the Outlook profile.

Deployment Considerations for Cached Exchange Mode

Because enabling Cached mode forces the end users to synchronize a full copy of their mailbox to a local OST file as well as a full copy of the OAB, the demand on an Exchange server can be quite high. If a large number of users must be configured to use Cached mode at one time, the best choices for configuring Cached mode are as follows:

  • Only enable Cached mode if the user will benefit from it. This would include traveling users or users who are on slow connections.

  • Deploy Cached mode to groups of users at a time rather than to the whole enterprise.

  • Encourage users to clean up their mailboxes prior to enabling Cached mode. Sent and Deleted items often account for 50% of the size of a mailbox.

  • Deploy Cached mode sooner rather than later. The smaller the mailbox at the time of the OST creation, the less data needs to be moved.

Using Cached Exchange Mode

Because Cached mode acts somewhat differently from a traditional mailbox, an administrator might consider some additional user training for those with Cached mode. This helps users recognize those differences and should result in fewer calls to the help desk. Some of these differences are mentioned in the following sections.

The Send/Receive Button

For users in Cached mode, it is unnecessary to click the Send/Receive messages button regularly when synchronizing with the new Cached mode functionality. This now happens automatically and clicking Send/Receive doesn’t accomplish anything.

RPC Over HTTPS and the Cached Exchange Mode

It is recommended that users running RPC over HTTPS also run with Cached Exchange mode enabled. This is because Cached Exchange mode deals better with “slow links and disconnections” to Exchange Server. Because RPC over HTTPS accesses Exchange Server information via the Internet, these users are more likely to experience network latency and slowness.

Slow-Link Connection Awareness

Cached mode was originally designed to address the challenges associated with links 128Kbps or slower. When slow-link connection awareness is enabled, it automatically implements the following email-synchronization behaviors:

  • OAB is not downloaded (neither partial nor full download).

  • Mail headers only are downloaded.

  • The rest of the mail message and attachments are downloaded when the user clicks on the message or attachment to open it.

To change the slow-link configuration, perform the following steps:

Click File.

Choose Cached Exchange Mode.

Uncheck On Slow Connections Download Only Headers.

Cached Exchange Mode and OSTs and OABs

Using Cached mode downloads a full copy of the user’s mail to the OST file stored locally on the user’s hard drive. However, administrators need to be aware of some considerations regarding OSTs and Cached mode to plan and make their configuration choices for these Exchange Server clients allowing optimal performance and efficient connectivity.

Cached Exchange Mode OST Considerations

OST files in Outlook 2007 use the new Unicode format. This allows them to go beyond the 2-GB limitation of the old American National Standards Institute (ANSI) format. However, be sure to account for the potential size of the OST file when planning your desktop or laptop images. Older notebooks might not have enough space locally to support a large OST file if you aren’t limiting the size of mailboxes on the Exchange server.

Cached Exchange Mode and Outlook Address Book (OAB) Implications

When using Cached mode, it is possible to download a No Details Outlook address book. However, users in Cached mode should download the Full Details OAB. This is because they can experience significant delays when they access the OAB when the full details are not locally accessible. When this situation occurs, the user’s workstation must contact the Exchange server to provide full data for the OAB. This results in delays for the user during the download.

When Cached mode is enabled, the OAB is synchronized every 24 hours, by default. If there are no updates to the server OAB, there will be no updates to the offline OAB. When there are changes to the OAB, only the differences are downloaded. This results in a faster update to the OAB for the Cached mode user.

Outlook Features That Decrease Cached Exchange Mode’s Effectiveness

Cached Exchange mode is easy to configure and provides many benefits to the occasionally offline user. It is important to try to keep the Cached mode experience as positive as possible for the user. Thus, it is useful to know that several Outlook 2007 features can actually decrease the effectiveness of Cached mode. The features discussed in the following sections all result in Outlook 2007 sending calls to the Exchange server for information when in Cached mode. For users using Cached mode, these calls can greatly decrease the effectiveness and performance of the client and, therefore, should be avoided if possible.

Delegate Access and Accessing Shared Folders or Calendars

These two items both require access to the Exchange server to view other users’ Outlook items. Cached mode does not download another user’s data to the local OST, so this nullifies the use of Cached mode when the functionality is required. These functions will work while the Cached mode user is connected to the Exchange server, but it can result in attempted external connections that will fail when the user is offline. This results in the interface waiting for a timeout before continuing with its processes.

Outlook Add-ins

Outlook add-ins such as ActiveSync can result in Outlook not utilizing important items, such as the Download Headers Only functionality that allows Cached mode to work so well. They also can cause excessive calls to the Exchange server or network. Avoid Outlook add-ins, if possible. Third-party add-ins should be tested with Cached mode for both online and offline behaviors to see if they are making calls to nonlocal data that could impact Cached mode users while they are offline.

Digital Signatures

Verification of digital signatures requires Outlook to verify a valid signature for messages sent using digital encryption, requiring a server call as well. Be sure to test such configurations to ensure that signed or protected content can still be accessed while a user is offline.

Noncached Public Folders

This, too, requires bandwidth and a call to the server. Consider synchronizing frequently used public folders to the OST through the use of Public Folder Favorites. Be careful not to cache too much public folder information because it inflates the size of the OST file.

Including Additional Searchable Address Books

If the enterprise includes custom address books and contact lists that are enabled to be searchable and usable for email addressing, this results in the client/server communications. These types of address lists are not cached by Outlook.

Customizing the User Object Properties

If the enterprise has created customized items on the General tab of the properties box of a user, this always requires a call to the server: When user properties are displayed, the General tab is always displayed first. Therefore, if these are necessary, consider placing any customized fields on a different tab on the user properties pages requiring a call to the server only when that tab is accessed, not every time the user properties are accessed.

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  •  Understanding Microsoft Exchange Server 2010
  •  Working with Email-Enabled Content in SharePoint 2010
  •  Enabling Incoming Email Functionality in SharePoint
  •  Getting the Most Out of the Microsoft Outlook Client : Using Outlook 2007 (part 3) - Using Group Schedules
  •  Getting the Most Out of the Microsoft Outlook Client : Using Outlook 2007 (part 2) - Sharing Information with Users Outside the Company
  •  Getting the Most Out of the Microsoft Outlook Client : Using Outlook 2007 (part 1)
  •  Implementing and Validating SharePoint 2010 Security : Using IPsec for Internal SharePoint Encryption
  •  Examining Integration Points Between SharePoint and Public Key Infrastructure
  •  Getting the Most Out of the Microsoft Outlook Client : Deploying Outlook 2007
  •  Getting the Most Out of the Microsoft Outlook Client : Implementing Outlook Anywhere
  •  Getting the Most Out of the Microsoft Outlook Client : Security Enhancements in Outlook 2007
  •  Getting the Most Out of the Microsoft Outlook Client : Highlighted Features in Outlook 2007
  •  Sharepoint 2010 : Deploying Transport-Level Security for SharePoint
  •  sharepoint 2010 : Verifying Security Using the Microsoft Baseline Security Analyzer
  •  sharepoint 2010 : Utilizing Security Templates to Secure a SharePoint Server
  •  Integrating Office Communications Server 2007 in an Exchange Server 2010 Environment : Web Conferencing
  •  Integrating Office Communications Server 2007 in an Exchange Server 2010 Environment : Installing and Using the Communicator 2007 Client
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