Can I use Outlook Cached Exchange Mode on XenApp and XenDesktop

You are driving a bus and you make a stop and pick up Margaret, a 66 year old woman. At the next stop, you pick up two people, a 22 year old man named Ralph and a 44 year old woman named Lisa. At the next stop, Margaret gets off, while 3 more people get on, a 35 year old man named Fred, his son who is 4 named Colby and a 32 year old woman named Heather. What is the name of the bus driver?

Did you get it? Was it too easy?

How about this one.

First, read through the Microsoft KB article that discusses where to store Outlook data files.

After reading it, can you tell me if Microsoft will support a configuration where Outlook is running on a RDSH (XenApp) or VDI (XenDesktop) instance in Cached Exchange Mode where the .OST file is stored on a networked file server?

Your answer will be based on how far you read. Unfortunately, I’ve witnessed many very bright people tell me that this configuration is not supported. The reason is that they were either told it wasn’t supported or they read this article and stopped before reaching the end. Why would they stop? Because in the “More Information” section of the article, only 1/3 of the way down says

It clearly states “Because of these behaviors, Offline Folders (.ost) files and Personal Address Book (.pab) files on a network share that are accessed remotely are also unsupported configurations.”

That is if you stop reading.

Further down, the article provides special statements for different circumstances. We are interested in the RDS/VDI section that says


So if I use RDSH (XenApp) or VDI (XenDesktop), I can use Cached Exchange Mode with the .OST file being on the network if I have a high-bandwidth, low latency connection. Well, that is our XenApp best practice, keep the data and app in close network proximity. So the network file server you use to store the .OST file should be in the same data center as the XenApp server, with this configuration, the location of the Exchange server become irrelevant.

Now should you implement it?  Stay tuned… 🙂

Blog Series Summary:

From the virtual mind of Virtual Feller

7 thoughts on “Can I use Outlook Cached Exchange Mode on XenApp and XenDesktop”

      1. So I’m with Carl on this one. As you said xenapp or XenDesktop should be in the same Datacenter as the application which in this case is Exchange and if that is the case then Why do I want to implement cached mode? I’m next to the exchange server, it is one more file in my home drive, one more thing that can get corrupted, and believe me I have seen corrupted OST files on physical machine.
        Maybe I’m just missing the use case for this configuration?


      2. Haha 🙂 my only gripe is that you have to use disk space for this. It will increase I/O to the file server (but hey isn’t that what they are there for) but having x GB for Exchange and times by 2 for OST’s means that IaaS customers will pay for data storage.
        (this is a very high level of why I prefer not to btw – i get the pros and cons).


  1. And remember note from Microsoft (from the same article):

    Note: Customers are responsible for both defining and maintaining adequate network and disk I/O. Microsoft will not assist in troubleshooting slow performance due to networked .pst or .ost files. Microsoft will only assist if the performance issue is reproduced while the .pst or .ost file is located on either a hard disk that is physically attached to the computer that is running Outlook, or on a virtual hard disk (VHD) that is attached to the virtual machine that is running Outlook.


  2. In Office 365 environments, cached Exchange Mode becomes very important, I think. I know that you can have a local Exchange server for caching, but it will never contain full mail boxes. In other words, having the Exchange server local is impossible. As far as I know (I have yet to learn more about Office365).


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