Friday, October 28, 2011

Outlook Cached Exchange Mode

Cached Exchange Mode is the process of when 2003/2007/2010 downloading a copy of the users mailbox and storing it locally on their workstation. This means all emails opened by the user from there onwards does not hit the Exchange servers significantly reducing load.

Many clients however still disabled cached Exchange mode on their users workstations. When asking them "why", their answer is always:

Because we need the user can access the most updated address book when they click the global address book.

If your company has this requirement this doesn't mean you need to disable Cached Exchange Mode. You can configure a registry key on your clients to simply keep the address book in online mode.

For more information on this key for Outlook 2003/2007/2010 please see:

Generally the only time you want to disable cached exchange mode is if your users run on a terminal services or Citrix shared environment where you do not want a copy of EVERY users mailbox downloaded and stored locally on the terminal server!


  1. " significantly reducing load". I wonder if anyone has proven that. As if all the synchronization activities don't take a lot of load.

  2. Try it for yourself. In a production environment disable cached exchange mode on all your workstations. Take a baseline of your exchange servers performance using perfmon. Then enable cached exchange mode on all your clients and take another benchmark. It is significantly higher.

    Everytime a user opens an email that has been read before, it pulls it off the server. With cached exchange mode it only ever pulls it once.

  3. We have users who use Outlook 2010 on workstations at work and via Citrix at home. How do we allow them to use cached exchange mode on their workstations at work, yet prevent them from using cached exchange mode via Citrix?

  4. Group Policy loopback processing my friend. However Outlook on a terminal server/citrix server should automatically disable cached exchange mode.

  5. How to turn off Cached mode on a terminal server???

  6. Outlook 2007

    [HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\Cached Mode]

  7. You do not need to turn of Cached Exchange mode for Citrix or Terminal Servers! If your server is Citrix or Terminal Services, Outlook will automatically disable cached exchange mode!