Best Practices of using Cached Mode in Microsoft Outlook 2003

Introduction

Cached Exchange Mode is a new great feature in Microsoft Office Outlook 2003. Cached Exchange Mode permits Outlook 2003 to use a local copy of a user's mailbox while Outlook 2003 maintains an online connection to a remote copy of the user's mailbox in Microsoft Exchange 2003. 

Upgrade

Upgrading client computers to Microsoft Office Outlook 2003 is a good idea and then enable Cache Mode (refer below Fig 1-1, here we enable cached mode in Outlook 2003). Cached Mode creates a local copy of the Exchange Mailbox and reduce the network traffic to the Exchange Server. This feature is great for Clients in remote Sites with limited network capacity. During the Migration process your users can work with the local copy of the mailbox.In any case Outlook 2003 is recommended seeing that it compresses information when working with Exchange 2003 and employs a useful Cache mode that works offline and synchronizes in the background with the server, better utilizing WAN lines.

Fig 1-1

Best Practices

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.

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:

1. Upload=dword:0000000f (default is 15 seconds).
2. Download=dword:0000001e (default is 30 seconds)
3. Maximum=dword:0000003c (default is 60 seconds)

The following features depends on network access and hence it can cause delays in Outlook (Cached mode) unless users have fast connections to Exchange data, so it is sugessted to limit those usage.

1. Delegate access (Accessing of e-mail by delegates )
2. Opening another user's calendar or folder
3. Using a public folder that has not been cached   

It is also recommended that you disable or do not implement the following features or combination of features if you deploy Cached Exchange Mode:

1. Instant Messaging integration
2. The toast alert feature together with digital signatures on e-mail messages
3. Multiple Address Book containers

In a typical scenario, 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.

Outlook 2003 add-ins: Remove Third-party add-ins if any. Sometimes third-party add-ins interfere with Outlook and cause performance issues.

Fine tune the Client-side rules such as:

1. Remove any unnecessary client-side rules.  
2. Click the Stop processing more rules option in the Rules Wizard.      

Impact of having Large Mailboxes:

1. If the user's OST file grows too large (for example, larger than 1 GB), Outlook with Cached Exchange Mode performance degrades. To improve response time in Outlook, users should either reduce the size of their mailbox (for example, by archiving older files) or turn off Cached Exchange Mode.
2. If the users' Public Folders Favorites folders include large public folders, their OST files can become large also, which can adversely affect Outlook performance in Cached Exchange Mode.
3. OST Offline File Folders.Unicode OST files can store up to 20 gigabytes (GB) of data, instead of the limit of 2 GB on non-Unicode (ANSI) Outlook files.
   

     4.  Users with large Exchange mailboxes

If users with existing OST files have large Exchange mailboxes, they might experience errors when Outlook attempts to synchronize their mailboxes to their OST files. To help prevent this, you can first set a policy requiring new Outlook files to be Unicode-formatted, since Outlook Unicode files do not have the 2-GB size limit that Outlook ANSI files do. Then, when Outlook is deployed with Cached Exchange Mode, Outlook creates a new Unicode OST file for users that currently have ANSI OST files. Users' existing OST (and OAB) files are not removed.

Some Issues that you may encounter

1. Outlook 2003 SP1 users in Cache mode have issues setting up OOF messages. (Even if you apply all latest updates. This issue is fixed in SP2)

2. When you use Outlook 2003 in cached mode and set a message for deferred delivery, the message is never delivered at the scheduled time, but when Outlook is launched

Note: Outlook 2003 in Cached Mode operates against a local .OST file which is synchronized with the server periodically.  When a message is deferred for delivery using "Do not deliver before" in the message options window, the message is deferred to the local Outbox instead of the server.  For this reason, the message will not be delivered from the local .OST unless the client is running at the time the message is scheduled to be delivered.

3. Delegate and Manager would observe inconsistent calendar details, if any of them is in Cached mode.

4. Users using Outlook in cached mode will not see the latest entries in the GAL immediately. Maximum delay that can happen is 24 hours. Again that depends on the OAB generation interval.

Summary

For optimal performance, you should use Cached mode in Microsoft Outlook 2003. This will dramatically speed up your experience using your Organization Exchange Server systems.  

Related Links

Cached Exchange Mode [1]
Enable Cached Mode in MS Outlook 2003 [2]