Offline access in Outlook Web App for Exchange 2013 lets users use Outlook Web App even when not connected to a network.
Offline access is newly available in Outlook Web App on the following web browsers.:
For more information about the offline user experience, see Using Outlook Web App offline.
Note: Users can’t search or sort messages while offline
Setting up offline access through a browser starts a process that copies mailbox data locally into a web database storage location. This is determined by the browser, and is typically a file or set of files on disk. For example, at the time this post was written, IE10 and Chrome browsers used the following file locations for their web database storage (on Windows):
The data stored for offline use is accessible through the Windows user account under which it is enabled, and is not encrypted. Like the other files on the computer, the best way to protect it is to use disk-level encryption such as Bitlocker.
By default, users are able to set up Outlook Web App 2013 for offline use. You can disable the ability for users in your organization to use Outlook Web App offline using the following Exchange Management Shell (EMS) commands:
To set offline access for an Outlook Web App mailbox policy, use:
Set-OwaMailboxPolicy –AllowOfflineOn [NoComputers | AllComputers | PrivateComputers]
To set offline access for an Outlook Web App virtual directory:
Set-OwaVirtualDirectory –AllowOfflineOn [NoComputers | AllComputers | PrivateComputers]
The browser’s local database stores some of the content of the Exchange mailbox. In Internet Explorer, this database is an industry standard HTML5 IndexedDB database. In Safari and Chrome browsers, this is a WebSQL database. The browser (not Outlook Web App) decides where the data is stored, what the quotas are, and how the data is ultimately aged-out. When Outlook Web App is set up for offline use, a process begins to copy all necessary Outlook Web App data locally. On a high bandwidth network, this process will often complete in a minute or two. Once offline is set up, the process will run whenever Outlook Web App is in use, and make sure that any server-side changes are reflected in the local database
This process iterates through the Exchange mailbox, getting and writing updates to the browser’s local database in the following order:
The amount of storage Offline Outlook Web App uses is bounded by the browser’s database quota. If the process hits browser quota while copying data, it pauses, and a back-off algorithm iterates through the above modules in reverse order, removing them from the local database until it is under quota.
Figure 1: Offline Storage Model
If the network connection fails or is disabled while Outlook Web App is in use, users can continue working normally. Similarly, a user can start Outlook Web App when offline, such as on an airplane or in a café without WiFi, and use it normally. Outlook Web App will appear without requiring that they sign in. The best way to get to Outlook Web App when offline is by using a favorite or bookmark. When Outlook Web App is set up for offline use, Internet Explorer will give the option of creating a favorite. The Favorite makes it easy to navigate to the right place. The only indication that the app is working offline will be a timestamp in the bottom corner of the Outlook Web App mail view indicating the last time that Outlook Web App was updated.
Other places that will differ between Outlook Web App in an offline vs online state are features that aren’t supported offline. For example, “Create Rule…” from right-clicking on a message, will show the same error message that would display if Outlook Web App was not setup for offline use.
When a supported action is taken while offline (for example, deleting a message), within a period of milliseconds the following sequence of events occur:
Figure 2: Offline Action and Data Synchronization Model
Outlook Web App determines network connectivity status based on the response of each web request to the Exchange server. As soon as network connectivity is detected, Outlook Web App replays the queue of offline activity back to the server, so that all clients will now reflect any work you’ve done while offline. After the queue is replayed and the server is up to date, the process to copy changes or new messages from the server to the local Outlook Web App database begins.
To store messages that were created offline, Outlook Web App creates an Outbox folder in the folder tree. This Outbox is local to the machine you’re on. Users can open and edit messages from the Outbox folder, at which point they become drafts and are moved to the Drafts folder until Send or Save is selected. Messages that are created and sent while offline will remain on the client until the next time Outlook Web App is open and connected to Exchange.
If the user regains network connectivity while working offline in Outlook Web App, they may be prompted to sign in again.