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Offline access for Outlook Web App (Exchange 2013 & Exchange Online)

Lets look at the new premier feature called offline access of Outlook Web App (OWA) in Exchange 2013 & Exchange Online.

This feature will be very useful when you have to work with a very low-speed or intermittent internet connection. Also user awareness is very important while using offline OWA, there are chances of all information being exposed. If an Administrator does not disable the option to use OWA in offline mode, users will be able to enable the feature on their own by clicking “offline options” in the drop-down menu on the right side of the screen. The process is designed very simple & users will only get the following warning:

“Do you want to allow office to use additional storage on your computer?”

Once we enable the OWA offline access, it will download all the data from the mailbox folders. Users can see Inbox, drafts & the folder that was viewed from the browser in last week. Also one can view & access calendar & contacts.

How does it work?

The browser has a local database in which it stores some of the Exchange Mailbox Content. This database is in WebSQL database is Chrome & Safari browsers, whereas in Internet Explorer it is an industry standard HTML5 IndexedDB. So we clearly understand that the browser is the one who decides on where the data to be stored, the quotas etc. So when Outlook web app is set up for offline use, it copies all web app data locally & this process will run whenever we use OWA in offline mode. OWA determines network connectivity based on response of each web request to Exchange Server. Soon after the network connectivity is established OWA replays the queue of offline process back to the server. After the queue is replayed the server will be up-to-date. To store all the offline messages OWA creates a Outbox folder in the folder tree. This Outbox is local to the machine in use & the user can edit messages in the outbox folder. Messages that are created & sent when offline will remain in the client until the OWA is open & connected to the Exchange Next time. Below is the process of OWA offline getting updates from the Exchange Mailbox

=> Data update for the currently displayed message list in OWA

=> Calendar notifications

=> Latest inbox list

=> Latest people updates

=> Latest calendar updates

=> Content of message in current list

=> Content of message in the rest of Offline-supported folders

=> In-line images in messages

=> Sync module – each item in the list above.

When it comes to the storage of the Offline OWA, it is purely based on the browser’s database quota. For instance if the process of downloading all items to an offline OWA hits the quota limit the process stops & it back-off algorithm through the above list of modules in the reverse order , removing items from the local database.

Below are the commands for Offline OWA access:

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]

Points to note:

=> Users can’t search or sort messages while offline

=> OWA offline is available on the following browsers:

Internet Explorer 10

Safari 5 or greater


=> If the network connectivity resumes while the user is working offline in OWA, the user will be prompted to sign in again.

Ratish Nair

Microsoft MVP | Exchange Server

Team @MSExchangeGuru

2 Responses to “Offline access for Outlook Web App (Exchange 2013 & Exchange Online)”

  1. Selvaraj Says:

    Exchange 2013 – email attachments from an external sender delivered as .bin files

  2. Prabhat Nigam Says:

    We would like to track down this issue. Can you share more about this issue?

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