Those who pay attention to details (unlike me often) might have noticed that Outlook 2013 rejoices in its ability to connect to email servers using Exchange ActiveSync (EAS). And then they ask the question why can’t they connect Outlook 2013 to Exchange via EAS? After all, if EAS is good enough for Hotmail (aka Outlook.com), why isn’t it good enough for Exchange? After all, EAS worked in the preview version of Outlook 2013, so the block was introduced between the preview and final version.
The answer is that Exchange absolutely will support EAS connections, but not from Outlook. In fact, Exchange probably supports more EAS connections from different devices than any kind of other protocol, largely because of Microsoft’s success in licensing EAS to vendors such as Apple, Google, and just about every manufacturer of an Android smartphone (this page provides a good overview of the various EAS client implementations).
But when it comes to Outlook connectivity, Exchange has a strong preference for MAPI, including MAPI when it’s securely wrapped in HTTP as in the case of Outlook Anywhere (aka RPC over HTTP), which is of course the predominant protocol for Outlook in Exchange 2013. Sure, it would be technically possible for Outlook 2013 to connect to Exchange using EAS, but Microsoft has blocked that option in code for very good reasons.
First, EAS is not as rich a protocol as is MAPI. Take a look at the functions available to EAS-enabled clients in your favourite smartphone and compare them to Outlook and you’ll conclude that Outlook, while perhaps a tad on the “fat client” side and somewhat bewildering at times in where it hides options, is a much more functional client than any smartphone. Don’t get me wrong here. I like using Outlook Mobile on my Windows Phone device, but it’s really still only for triage given the volume of email that I receive and need to process daily.
Second, although Outlook supports online mode that could be used with EAS, I doubt very much whether cached Exchange mode would work. And cached Exchange mode is the most heavily used form of connection for Outlook clients. In fact, I don’t think I have used Outlook in online mode since Outlook 2003 introduced cached Exchange mode ten years ago.
Third, Exchange has an infrastructure called Outlook Anywhere (OA) that’s designed to cope with Outlook connections. Yes, the Client Access Server also accommodates EAS connections and, at first blush, they seem similar. But I hazard a guess that OA has been tweaked and refined since its introduction in Exchange 2003 SP1 to make it robust, reliable, and fast performing. EAS was introduced in Exchange 2003 SP2, so it’s only a year younger than OA, but OA has seen a lot more client connections since, largely because mobile EAS clients have only really taken off in the last four years or so. Before then, the major story in Exchange mobile clients revolved around RIM’s BlackBerry devices and the constant struggle that administrators had to tame the BlackBerry Enterprise Server. Times have certainly changed.
I've also heard from Dave Stork that Microsoft has blocked EAS connections from Outlook 2013 to non-Microsoft email servers such as Zimbra and Zafara. I have no tested whether such a block exists but it doesn't surprise me if one does.
There are edge cases when you’d imagine that EAS might be a good way for Outlook to connect. But then you look at the horrible Windows 8 Mail app that can connect to Exchange using EAS. If allowing Outlook to connect to Exchange via EAS made it behave like Windows 8 Mail, I think I should immediately look for another client. Even Gmail (only kidding!).
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