Exchange, EAS, and Outlook 2013

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, 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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Discuss this Blog Entry 3

on Jan 10, 2013
And now Blackberry 10 will be using EAS instead of MAPI to connect to Exchange. So, that's another one for the list.
on May 21, 2013

We have a custom CRM system. This is a large scale enterprise LOB application.

Our customers have been clamoring for syncing options. Mobile devices, Outlook, and gMail top the list.

We have been working on implementing an ActiveSync implementation using the ZPush stack. I was disappointed enough to discover that Outlook 2010 and earlier didn't support EAS, but was happy and content that 2013 would support it.

However, when trying to test this, I started getting error messages, which led me to this blog. Are you telling me that technically it works, but MS has blocked it?! For what purpose? I can understand that they would prefer you to use something else to connect to an actual Exchange server, but this isn't Exchange!

Any help or suggestions?

on Jan 18, 2016

Our organization is currently running Zimbra Network Edition 8.0.8 on a split domain with Exchange 2003 as the primary. Just a few min. ago I had a user who had 2013 outlook. "First user in our environment" Zimbra comes with a connector zco "zimbra outlook connector" and I was told by Zimbra its was compatible with 2013 but I was getting an error that it could not find outlook, so the connector would not install. I then realized on outlook you can select EAS and I was able to make it work with our Zimbra server. .....Update 01/18/16 So weeks later I realized email works fine but the address book does not work.

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On-premises and cloud-based Microsoft Exchange Server and all the associated technology that runs alongside Microsoft's enterprise messaging server.


Tony Redmond

Tony Redmond is a senior contributing editor for Windows IT Pro. His latest books are Office 365 for Exchange Professionals (eBook, May 2015) and Microsoft Exchange Server 2013 Inside Out: Mailbox...
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