Using OWA offline mode for expanded Outlook access in Exchange 2013

By Brian Posey,

Until recently, Outlook offline was only available to Outlook users. Organizations using Outlook Web App (OWA) for email access were left out in the cold when it came to offline access. In Exchange Server 2013, Microsoft introduced offline access for OWA users.

In Exchange 2013, OWA offline access is enabled by default; if you want to disable OWA offline, you need to use the Exchange Management Shell. Exchange Server 2013 allows you to control OWA offline access based on mailbox policies or on OWA virtual directories. Offline access can be granted to no computers, private computers or all computers. For example, you'd use the following command to set the OWA mailbox policy to allow offline access only to private computers:

Set-OWAMailboxPolicy –AllowOfflineOn PrivateComputers

Similarly, you could use another command if you wanted to block OWA offline access for the OWA virtual directory:

Set-OWAVirtualDirectory –AllowOfflineOn NoComputers

If you wanted to allow unrestricted access to OWA offline mode later on, you could use the same command as before, but set the –AllowOfflineOn parameter to AllComputers.

In OWA offline, the Web browser does all the work

When I've had the opportunity to talk about OWA offline access, the same questions come up. People often ask where the cached data is stored and how much space the cached data consumes. Unfortunately, there are no straightforward answers to these questions because the end user's Web browser does all the work. The Web browser controls the path where cached data is stored and also sets the quota for how much cached data can be stored on a Web client.

The browser even controls the data repository. For example, Internet Explorer 10 stores cached OWA data in an IndexedDB database (which is an HTML5 standard), while Safari and Chrome use a WebSQL database.

The OWA cache is different from the Outlook cache

One of the most important things to understand about OWA caching from the end user standpoint is that it works differently than Outlook's caching feature. In Outlook, a user's mailbox data is cached to an OST file because OWA offline mode uses a browser database instead. The content database type is not the only difference; there are also major differences in the actual cached data.


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