Improvements in Client/Server Communication in Outlook 2003 and Exchange Server 2003


Topic Last Modified: 2005-05-18

The more mailboxes an organization places on a single server, the more client connections the server must manage. Consequently, optimizing client/server communication is an important aspect of server consolidation. Microsoft® Office Outlook® 2003 is an ideal messaging client for Exchange 2003. This client contains numerous features that are specifically designed to reduce network bandwidth consumption and improve the e-mail experience of users over remote connections in an Exchange 2003 organization.

The following are key improvements that you can make in client/server communication by using Outlook 2003. These improvements enable you to place a large number of mailboxes on a single server running Exchange 2003:

  • MAPI compression and buffer packing   When you use Outlook 2003 in an Exchange 2003 organization, mailbox content is compressed on the Exchange server before being sent to the Outlook 2003 client. In addition, the data is packaged in large, optimized buffer packets, thereby reducing the number of requests that must be transferred over the network between the Outlook client and the server running Exchange 2003. Both MAPI compression and buffer packing significantly lower the network bandwidth requirements for client/server communication and enable an Exchange server to manage an increased number of users with acceptable response times.

  • Exchange cached mode   This feature enables Outlook 2003 to download all items from the server-based mailbox and keep them synchronized in a cache on the local client computer. After a full copy of the mailbox is downloaded, the client performs most e-mail related tasks from the local computer. Communication with the server is only required during offline folder synchronization, when downloading new items to the client computer, when uploading added or changed items to the server, or when sending messages. The following figure illustrates the Exchange cached mode principle.

    Synchronizing server-based mailbox content in Exchange cached mode


    Exchange cached mode can potentially reduce both the workload of servers and the consumption of network bandwidth. Exchange cached mode also improves the remote or branch office user's experience of Outlook 2003. Access to items stored in the local cache is always fast, no matter how slow or unreliable the network connection, and access to the items stored in the local cache does not depend on server availability. Because the client works with a local copy of the data, users do not need to restart Outlook 2003 to an offline profile when network interruptions occur or when the server is shut down temporarily for maintenance reasons.

    In Exchange cached mode, users can choose from the following download options.

    • Download full items   This is the default setting and the best option when you use Exchange cached mode over fast and reliable network connections. The client downloads all items to the client immediately.

    • Download headers first and then full items   In this option, the client first performs a header download, so that users can immediately see a list of new items. Following the header download, the client performs a full download to bring all data to the client. This option might be a good choice if users want immediate access to new messages, but note that this mode requires an extra cycle of client/server communication compared with downloading full items.

    • Download headers only   This is the best option when you use Exchange cached mode over slow and unreliable network links, such as dial-up connections. The client downloads the message headers only, so that users can see the size of e-mail messages and attachments, and then decide which items to download or delete directly on the server. The client downloads a message when users open it in Outlook 2003.

    Because of its many advantages, it is recommended that you enable Exchange cached mode over local as well as remote network connections.
  • Improved Outlook 2003 synchronization performance   Outlook 2003 performance in Exchange cached mode is further improved by reducing the number of change notifications between client and server. The server informs the client about the number and size of messages to be downloaded, and when items are marked read or unread, are flagged, or are modified in other ways, only the header listing the change is sent back to the server. When full items are downloaded, MAPI compression ensures efficient data flow.

    It is important to understand that the synchronization in Outlook 2003 is incremental. That is, if a synchronization cycle is interrupted, the synchronization process resumes where the interruption occurred, instead of resuming the entire synchronization process. Items marked as corrupted or conflicting are moved to the Sync Items folder, allowing synchronization to continue. Users see a synchronization progress meter in the lower right corner of the Outlook 2003 client. The progress meter shows detailed synchronization information, such as the total amount of data left to synchronize, and whether the mailbox folders are up-to-date.

  • Outlook 2003 performance monitoring   Outlook 2003 collects performance information and sends it to Exchange 2003 so that an Information Technology administrator can identify performance bottlenecks relating to poor bandwidth conditions or poor connectivity. The performance data is stored in the Exchange store, as well as reported in the event log and through performance counters. To monitor response times on a continuous basis and to create performance reports over any period of time, you can use either non-Microsoft tools or Microsoft tools, such as Exchange 2003 Management Pack (Exchange Management Pack.akm) for Microsoft Operations Manager. Analyzing the performance data on a centrally located server can help an Information Technology department identify when local and remote clients are experiencing connectivity issues.


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