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.
Prior to the Outlook 2013 release, the full contents of a user's mailbox were cached to an OST file. This changed slightly in Outlook 2013 when Microsoft took measures to reduce the size of OST files. Even so, Outlook 2013 caches practically anything a user could access while working offline. This simply isn't the case with OWA.
When an OWA user works offline, he sees all of his mailbox folders but only the offline supported folders will display content. Offline supported folders include the Inbox and Drafts folders as well as any other folder the user accessed within the last week.
This isn't to say OWA will cache the user's entire inbox. OWA only caches the last three days of content or the last 150 items, whichever is larger. Email attachments are not cached.
Calendar access works in nearly the same way as when the user works online. Users still get their calendar reminders and can access calendars for the current month and the upcoming year. However, there is no option to view multiple calendars when working offline because calendars are not cached.
Users also have full access to their contacts while working offline. Likewise, the auto complete list is also cached.
For the most part, OWA offline access works really well. Users can create new messages or open cached messages, and there is even full offline support for Information Rights Management protected content. Similarly, OWA provides offline access to a user's calendar and contacts. The biggest restrictions are that OWA caches a limited amount of data and requires a supported browser.
About the author:
Brien Posey is an eight-time Microsoft MVP for his work with Windows Server, IIS, Exchange Server and file system storage technologies. Brien has served as CIO for a nationwide chain of hospitals and health care facilities, and was once responsible for IT operations at Fort Knox. He has also served as a network administrator for some of the nation's largest insurance companies.