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Microsoft Announces Exchange ActiveSync v16

When Exchange Server 2013 shipped it was noted by some (such as MVP Dave Stork) that there were no apparent changes to Exchange ActiveSync when compared to Exchange Server 2010. In fact, some had speculated that ActiveSync would not be developed any further and may even be deprecated in favor of newer mobile device management features.

So it may come as a surprise to read the announcement by Microsoft of Exchange ActiveSync v16, currently planned for roll-out in Office 365 and inclusion in Exchange Server 2016. The updated protocol has three new capabilities included:

  • Enhanced calendar reliability brought about through a reworking of the calendar workflow between server and client. End users won’t notice this (except perhaps the intended outcome of fewer calendar issues), but I imagine that administrators will be very happy to receive fewer support calls about calendar problems.
  • Syncing of calendar attachments. A curious inclusion when you consider the big push to go “attachment-less” in email, but I suspect it is far too early to expect widespread uptake of the new way of doing things, so if ActiveSync devices can sync calendar attachments now without backend servers crumbling under the weight of extra sync traffic then I’m all for it.
  • Syncing the drafts folder. It’s the little things that make the biggest differences to end users 🙂

When will the new protocol be available in Office 365? Microsoft says you can check the supported ActiveSync protocols for your mailbox by running the ActiveSync test on the ExRCA site.


But first your mobile device/client must be updated to support the new protocol as well. Microsoft has already confirmed that iOS9 (announced at the recent WWDC event) will support EAS V16 in the Mail app. No word yet on support for other platforms, but I suspect that support in Outlook for iOS and Android won’t be far away.

Paul is a Microsoft MVP for Office Servers and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul is a co-author of Office 365 for IT Pros and several other books, and is also a Pluralsight author.
Category: Blog


  1. LAN Admin says:

    Our iOS version 9.1 devices do not appear to be negotiating with EAS v16 in O365.

    The ActiveSync Protocol logs show the iOS client RequestHeader returns: MS-ASProtocolVersion: 16.0

    The ResponseHeader however returns:

    X-MS-RP: 2.0,2.1,2.5,12.0,12.1,14.0,14.1,16.0
    MS-ASProtocolVersions: 2.0,2.1,2.5,12.0,12.1,14.0,14.1,16.0
    MS-Server-ActiveSync: 15.1


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