Blocking Online Mode Outlook Connections In Exchange 2007…

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A question that comes up in various forums is to find a way to block all “online mode” outlook connections in the network. As we all know, Outlook can work in online and cached mode. Online mode puts more load on the exchange server. It isn’t that significant if you are a small company. But with higher number of concurrent mailbox sessions, the server performance will be affected for sure.

The ideal solution is to force everyone to use Outlook in cached mode by blocking the online mode altogether. With Powershell, the task is very easy. Run

Get-CASMailbox –Resultsize Unlimited | Set-CASMailbox –MAPIBlockOutlookNonCachedMode $true

We use –Resultsize as only 1000 items are returned by default. It won’t do any harm even if you use it in a network with less than 1000 users.


If you want to use the online mode for yourself, you can always run the same command to change the setting. For example, if I want my account to be able to use the online mode, I would run

Set-CASMailbox –identity “Rajith” – MAPIBlockOutlookNonCachedMode $false

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About the author: UC Architect, Blogger, Husband & Dad. I have been in IT for the last 12 years, with Exchange Server becoming the prime area in the last few years. I am active on Experts Exchange & TechNet forums and I am a technical author for SearchExchange.

2 comments… add one

  1. Marc

    Would this setting Set-CASMailbox –identity “Rajith” – MAPIBlockOutlookNonCachedMode $false
    meen that the mailbox will not cache at all?

    As this is what im looking to find out is there a powershell command that can stop a mailbox from caching.

    1. Rajith Enchiparambil

      Hi Marc,

      The command Set-CASMailbox –identity “Rajith” – MAPIBlockOutlookNonCachedMode $false means that you are not blocking outlook online mode.

      You can use group policy to block cached mode, check

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