For the longest time (read: forever), we were led to believe that Outlook simply does not run in Cached Mode on Windows Terminal Servers. But that has actually changed with Outlook 2010 and Server 2008 R2. This does not mean that you should deploy Outlook 2010 in Cached Moe on your Server 2008 R2 XenApp servers, but it means that you could. From a Microsoft Technet article:
To achieve optimal results when you use Outlook with Remote Desktop Services, pay attention to how you customize your Outlook configuration. For example, in Outlook 2010 you can configure Cached Exchange Mode with Remote Desktop Services.
The article is careful to mention that you’d need to have enough disk space on the server to handle each user’s OST file. Maybe this makes sense for small environments with only one Terminal Server and tidy mailboxes. I can count on less than one hand how many firms fall into that category.
Based on our experience, we recommend disabling Cached Mode on any XenApp server we put in place. At the same time, we want to allow our users to run in Cached Mode on their Windows 7 desktops. How do we achieve this? Through the use of Loopback Policy, we can ensure that when users log in to a XenApp server, Cached Mode will be disabled. This policy will override the settings within a MAPI profile that is roamed or flexed to the XenApp server. When the user logs back into their Windows 7 desktop, they are happily working in Cached Mode again.
This is just another example of how technology can change without much fanfare. For many years, we never hard to worry about this situation. The mere fact that the user was logging in to a Terminal Server with Outlook 2003 meant that Cached Mode would be disabled no matter what. But with Outlook 2010 and Server 2008 R2/XenApp, a successful implementation relies on a successful configuration of the environment. You can download the Microsoft White Paper on the planning considerations of Outlook 2010 on Server 2008 R2 here.