As a network administrator, you may find yourself tempted to turn on the group policy setting that would force all Outlook users to operate in Cached Mode, to save on network bandwidth.

However, those who have turned that setting on in a production network know that it can have the opposite effect – it will literally bring a network to its knees as all clients everywhere will attempt to download a copy of their inbox to sync a local .OST file with the server mailbox.

That will keep most network admins from turning this setting on – so how would you go about turning this on without negatively impacting performance?

The following scenarios include examples of how you could deploy Cached Exchange Mode to avoid a large initial performance impact on the Exchange servers and—in some cases—minimize the time users spend waiting for the initial synchronization:

  • Retain Outlook OST files while deploying Cached Exchange Mode. Since existing OST files are merely updated with the latest mailbox information when Outlook with Cached Exchange Mode starts for the first time, retaining these files when you deploy Cached Exchange Mode can help reduce the load on your organization’s Exchange servers. Users who already have OST files will have less Outlook information to synchronize with the server. This scenario works best when most users already have OST files that have recently been synchronized with Exchange Server. To retain OST files while you deploy Outlook with Cached Exchange Mode, do not specify a new Exchange server when you customize Outlook profile information in the OCT. Alternatively, when you customize Outlook profiles, clear the Overwrite existing Exchange settings if an Exchange connection exists (only applies when modifying the profile) check box.(If you specify an Exchange server when you configure and deploy Outlook with this option enabled, Outlook replaces the Exchange service provider in the MAPI profile, which removes the profile’s entry for existing OST files.)

  • Provide seed OST files to remote users, and then deploy Cached Exchange Mode after users have installed the OST files you provide. If most users in your organization do not currently have OST files or are not using Cached Exchange Mode, you can deploy Office Outlook 2007 with Cached Exchange Mode disabled. Then, before the date on which you plan to deploy Cached Exchange Mode, you provide initial or "seed" OST files to each user with a snapshot of the user’s mailbox; for example, by providing or mailing to the user a CD that contains the file with installation instructions. You might also want to provide a recent version of your organization’s Office Address Book (OAB) with Full Details. You configure and deploy Cached Exchange Mode when users confirm that they have installed the files.

  • When you update your Outlook deployment to use Cached Exchange Mode later, the Exchange server updates users’ existing OST files and there is much less data to synchronize than there would be if a new OST and OAB were created for each user. Creating individual CDs for each user’s OST file can be time consuming, so this procedure might be most useful for select groups of remote users who would otherwise spend a lot of time waiting for the initial mailbox and OAB synchronization, perhaps at a high cost, depending on their remote connection scenario.

    Here are the step by step instructions on seeding an OST file.