You can now launch Outlook Web App (OWA) in the browser and start working even if there is no network connectivity. The work you do while disconnected is automatically synchronized the next time connectivity is restored. This allows you to be productive using OWA even when you have no network connectivity. It also makes OWA faster and a better experience from remote locations with slow or intermittently connected networks.

Our goal for OWA offline is to support the most common user actions, as far as HTML5 offline capabilities allows. This does not take us to the complete offline support of Outlook on the Windows or Mac desktop, but it matches or exceeds the offline capabilities offered by most Exchange ActiveSync phone clients.

Most email triage and calendar management actions work in OWA while offline. You can:

• send email and calendar invites
• delete email
• get reminders
• decline meetings
• flag and categorize messages
• etc.

The offline capability in OWA makes most of your email, calendar and contact information available offline. Some of the available features and limitations are:

• The last few days of messages. Supported folders include Inbox, Drafts and any folder viewed within the last three days, up to 15 folders
• The previous month and future year of your Calendar
• A limited set of upcoming Calendar reminders (2 months)
• All of the items in your Contacts folder, plus any people that you email often and any that you have emailed recently
• Offline access does not include archived folders, team folders or tasks
• Full-text indexed search is not yet possible with OWA offline, or HTM5 offline in general

You can enjoy OWA offline in IE10+, Chrome 17+ or Safari 5. Over time as the offline capabilities of browsers mature, so will OWA’s offline capabilities  You must enable OWA offline functionality on every computer where you want to be able to use OWA without network connectivity. Administrators have the ability to control which users can use OWA offline.

To enable OWA Offline

1. Log into Office 365 Preview, click "Outlook" to launch OWA, open the Options menu next to your name in the to right corner of the browser and then click "Use mail offline"
   
   
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2. OWA will inform you that the OWA data you are about to cache will be available for all users who log in under the account you are currently using on the PC (Internet Explorer will store the data in %systemdrive%\Users\%username%\AppData\Local\Microsoft\Internet Explorer\Indexed DB) If you are ok with that (e.g. if you are the only person logging in under the account) click yes to proceed..
   
3. OWA will suggest to you, that you add OWA to your Favorites for easy accessibility
   
4. Name the entry for OWA in your Favorites
   

Using OWA Offline

Now imagine a scenario where you are working on your messages in OWA, and suddenly connectivity is lost

Even if in a no connectivity situation, you can continue working in OWA e.g. compose a new mail

Write the mail and choose the recipient(s). In this example I'm working from my Office 365 Preview account (on my Office 365 Preview tenant @modernoffice.onmicrosoft.com) and I'm composing a mail to my everyday work email @microsoft.com. I hit send and continue working on other tasks.

Now imagine a while later, when connectivity is restored, I open OWA 2010 to read my work mail and sure enough - the mail sent in the Offline scenario is there for me to read (see left side of graphics below).

Caching 

OWA offline is enabled via a new feature in IE10, called Cache and databases. To access the settings for the cache

1. open "Internet Options"
2. click the "General" tab
3. click the "Settings" button to open the Website Data Settings dialog
4. click the "Caches and databases" tab

 From here you can e.g delete the cache (will disable OWA Offline) or change notification settings.

Note:

• You can enjoy OWA offline in IE10+ (using HTML5’s IndexedDB for storage), Chrome 17+ (with WebSQL) or Safari 5 (also using WebSQL)
• At the time of writing this article (august 28, 2012) the 'boot from offline' scenario (booting IE in a no connectivity environment) does not work in my Office 365 Preview (Beta) environment. But its expected to work after the beta.

See also

• Offline access in Outlook Web App 2013 - link (deep dive from the product group - Nov 6th 2012)