What should we make of the introduction of offline mode for Outlook Web App 2013? Will it be useful in practice or is it simply another example of a “me too” feature included to keep Exchange Server 2013’s browser client competitive with Gmail Offline, the equivalent feature offered by Exchange’s major opponent, Gmail. Exchange could be regarded as being a little late to the offline party as Gmail has had offline capability since November 2011.
Right now it’s a little early to say because few people are using OWA 2013 in anger. Things will only really begin to clarify when companies start to deploynext year, soon after the release of the interoperability bits necessary to allow Exchange 2007 and Exchange 2010 to co-exist alongside the new kid on the block.
Update (Oct 2014): Clearly things have changed since this article was written and many people are now using OWA offline with Exchange 2013 and Exchange Online (as part of).
For now we can only make an initial assessment based on testing and the information released by Microsoft such as the informative post on the EHLO blog. With that in mind, let’s consider some of the most important aspects of OWA offline.
First, the capability is built on top of industry standards and isn’t something invented by Microsoft. As I noted in a post last April, the W3C “IndexedDB” API is key to OWA Offline. This industry effort has contributions from Microsoft alongside Mozilla and Google to set out methods for the storage that browsers can use to cache data offline, similar in a simpler respect to the way that Outlook caches replicas of mailbox data in its offline storage file (OST).
Second, because IndexedDB is a relatively new API, it follows that only modern browsers are capable of offering offline access. If you’ve made the bold decision to deploy Windows 8, you’ll be all set as IE10 is one of those browsers. Microsoft released a preview version of IE10 for Windows 7 on November 13 and signs are that the final version should be available soon. We shall see. Of course, you have the option to deploy Chrome on Windows as the latest versions (I’m running version 23.0.1271.64 as I type this) support offline access. And there’s Safari 5 for those who run on Mac, but not Safari for Windows. Firefox and Opera users are out of luck so far.
Third, the issue of how to secure mailbox data cached by the browser is bound to furrow the brows of security professionals. Outlook doesn’t get so much heat on the subject if only because an OST can only be opened by a MAPI client that has the right credentials, but the caches maintained by browsers might be a more obvious target for those who like to browse for “interesting” information. And the prospect of users innocently activating offline mode on kiosk browsers is enough to bring the security crowd out in a cold sweat. Some control can be gained through OWA mailbox policies, which support the ability to restrict offline access on a per-user basis or limit access to “private” computers. Bitlocker offers some comfort in terms of data encryption on client PCs if this is deployed. If not, it certainly should be if you’re going to allow people to use OWA offline.
Fourth, users might need some education to understand exactly what data is available when offline. For instance, the calendar caches the current month and all events through the end of the year, which is fine as long as you don’t want to check on what you did last month. Only 3 days of content or 150 items (whichever is larger) are cached for each of the folders available offline and attachments are not downloaded as this could increase the time and bandwidth required to populate the cache. The Inbox folder is always available as is any folder viewed through OWA when online over the past week. Again, easy enough to understand provided you’re told – and remember, which might not always happen when searching frantically for an item that you need in a hurry! And although your People (aka Contacts) are available, there's no notion of an Offline Address Book for use by OWA when it is offline.
Other restrictions exist when working offline, mostly because a feature such as MailTips absolutely needs to have access to Exchange to operate. But these are small points that users will quickly forgive in the light of the additional value that they can potentially gain from offline access. It will be interesting to see how things work out as people start to use OWA offline. And like almost every other initiative we have seen Microsoft introduce into Exchange over the years, you can expect OWA offline to improve and mature in terms of functionality, usability, and performance. We shall see!
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