I often get asked about the advantages and drawbacks of using Cached Exchange Mode. With differing customer needs and environments, the answer is not one-fits-all, so here is my short list to answer the question of should you use or not use cached Exchange Mode.
Non-Cached Mode is considered “Online” mode – everything stays on the server.
Cached Mode keeps a master copy on the server and brings a copy local so that if Exchange is not accessible, one can still view personal Outlook Mail, Calendar, etc. Outlook automatically manages your server connection and data updates; when your connection is restored, Outlook synchronizes your cached mailbox with your mailbox on the server.
If users have roaming profiles and expect to use Outlook on different machines, I don’t use Cached Mode. This would initiate a local dump of the Exchange mailbox to each local machine used. This creates unnecessary network traffic and is not very secure – having copies of all your mailbox floating around that is.
If security is a concern, especially on laptops, I don’t typically do Cached Mode. It’s really easy to change a users’ password in the event a laptop gets stolen, but what’s the point if the thief has all the time in the world to hack the OS login or use a different method to grab the OST file? If this is required, definitely use Bit Locker or some encryption of the Outlook files to help reduce the impact.
If your users access Outlook through a Terminal Server session, don’t use Cached Mode. Not to worry, as you can’t enable Cached Mode on Outlook when installed for this purpose anyway.
Obviously, having users still able to open their Outlook clients and view their world is a huge positive. Having this feature turned on has saved my bacon on more than one server reboot parties.
In Exchange / Outlook 2010, there are several features that require Cached Exchange Mode:
•Junk E-mail Filter
•Conversation View (Show Messages from Other Folders)
•People Pane / Outlook Social Connector
Aside from Cached Exchange Mode, Instant Search also needs Windows Search in order to work. The Outlook Social Connector, which adds the People Pane in Outlook, relies heavily on Instant Search.