Sunday, November 12, 2006

Exchange Cache Mode - Good and Bad

Outlook 2003 has a great feature called Exchange Cache Mode. According to Microsoft,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.

Putting the Outlook email client into cached-mode enables several functions designed to lessen the dependence of a connection between the Outlook client and the Exchange server. Such as creating a local copy of the GAL and a local copy of the users INBOX all allow more of the users interaction with their mail client to take place on their workstation (even if the connection to the mail server is unavailable.) This means a reduced amount of interactive network traffic back to the mail server.

In many situations, this is a very good thing. Laptop users are a wonderful example of users who need to be able to work with their email even when they are not connected to the network. Another would be users whose mail box is not local but is accessed over a WAN, VPN or dial-up link where the user experience when interacting with the mail server over a slow link would not be a good one.

There can be a down side to using cached-mode, however. Situations where users need to interact with another users mail information such as sharing of calendar information. Or where there is interaction with another application like ActiveSync or Blackberry. These and other problems are documented by Microsoft and others so the problems are well known technically.

Instead of a blanket Outlook cache-mode for everyone, a better and more supportable recommendation would be the following:

Good candidates for Outlook cache-mode:
*Portable devices (tablets, laptops, etc.) where the user typically is accessing Exchange services at less than LAN speeds (WAN, VPN, dial-in)
*Users in locations without a local Exchange server and access a mailbox over a WAN link.

Bad candidates for Outlook cache-mode:
*Blackberry users
*ActiveSync users
*Users who have given delegate control to other users over their mailbox/calendar
*Users whose mailbox is located on an Exchange 2000 server
*Users who have client-side rules to be run
*Users who are about to have their mailbox moved to another mail server

The Microsoft article can be used as a reference as this has both instructions for enabling Outlook cached-mode but there is also a section labeled "Practices to avoid when you use Outlook 2003 with Cached Exchange Mode" that should be reviewed.

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