Announcing Exchange ActiveSync v16

One advantage of having your mailbox in Office 365 is that we usually deploy our innovations there first. We’re making enhancements to Exchange ActiveSync (EAS) in Office 365 that will soon be available to Exchange ActiveSync applications. Update: Exchange ActiveSync v16 will also be included in on-premise installations of Exchange Server 2016.

Updated EAS, which we will call version 16, contains three new major capabilities:

  1. The major focus is enhanced calendar reliability brought about through a reworking of the calendar workflow between server and client. This is a major benefit but ideally will be largely unnoticed by end-users. Success here will be the absence of those hard-to-diagnose calendar related problems sometimes seen when the server and client are not produced by the same company.
  2. Calendar attachments. Previously calendar items synced with EAS could not include any attachments such as agendas, decks or spreadsheets. In version 16 that is now possible.
  3. Syncing the drafts folder was previously not supported. We’ve added that support in version 16. Now you can start an email on your EAS device and continue editing that draft back at your desktop by retrieving the mail from the drafts folder. Or, write your draft at your computer, then make the final tweaks and send it from your phone while you're on the go.

Customers with their mailbox in Office 365 can take advantage of these new features when their favorite EAS client is updated. Update: We are happy to share that iOS 9, announced June 9 at Apple’s Worldwide Developer Conference, will support the calendar features of version 16 when it is released this fall.

As an end user, how can you tell if your mailbox is enabled for EAS version 16? The simplest way is to run an "Exchange ActiveSync" test at and look for version 16.0 listed as one of the supported protocol versions (MS-ASProtocolVersions header in the OPTIONS command response) in the test results. Note that you need a valid Office 365 email address and password in order to run that test, and the results are specific to that mailbox only (not the entire tenant).

Update: For partners who are building Exchange ActiveSync applications, preview documentation for EAS v16 is now available at

Note to developers: Exchange ActiveSync is different from the Office 365 Outlook REST APIs. Exchange ActiveSync is highly optimized for mobile clients connecting directly to Office 365/Exchange Online, and requires a licensing fee to use. The Outlook REST APIs are standards-based REST+JSON+OAuth Mail, Calendar, and Contact APIs that have no licensing fee, and are great for both mobile device-to-Office 365/Exchange Online, and service-to-Office 365/Exchange Online applications. We recommend that developers explore and evaluate the Outlook REST APIs for their applications.

Comments (29)

  1. MaxM. says:

    Will it be possible to see a colleague's shared calendar from an EAS device?

  2. @MaxM: I asked, and unfortunately access to other people's calendars is not part of the planned features for v16.

  3. Doug says:

    Will EAS v16 be available on-prem with Exchange 2016 or any version of Exchange?

  4. @Doug: Yes, it will be in Exchange Server 2016. I'll add an update to the post to reflect that.

  5. MaxM. says:

    Personally I don't understand how it is possible that, in 2015, in a world where collaboration is so important, Exchange On-Prem/Online does not allow access to shared calendars yet. All of my clients are asking for this feature since Exchange 2007….. really I can't understand…

  6. CG says:

    Will EASv16 support Archive Mailboxes?

  7. Theo says:

    Will it only be Exchange Server 2016 that will support EAS v16 or will it also be made available to earlier versions of on-premise Exchange ?

  8. Currently there are no plans to implement v16 in earlier versions of Exchange Server.

  9. Naresh says:

    i dont see any mention about calendar attachments in the preview spec, can you help me point to the exact specification?

  10. Anku says:

    Thanks for the post.

    You can also check for office online support

  11. Qaas says:

    Jason, as you have pointed out here in your blog post – I ran the AutoD test for EAS thru RCA site for my O365/EXO mailbox, but in the results I don't see anywhere any mention of version of EAS being advertised by the server as supported protocol versions. Can you please explain how to get that info from that test with an example, including the current version (v14 or v15) and then how it should look iif one has support for v16. At least mention the current one, if you can to give us an idea quickly. Thanks!

  12. @Qaas: My apologies, the post is a bit misleading. You should run the "Exchange ActiveSync" test, NOT the "Exchange ActiveSync Autodiscover" test. Once that's run, expand "Test Steps", then under "An ActiveSync session is being attempted…" expand "Test Steps". Then under "Attempting to send the OPTIONS…", expand "Additional Details." Look for the MS-ASProtocolVersions header in the results there. It should look like:

    MS-ASProtocolVersions: 2.0,2.1,2.5,12.0,12.1,14.0,14.1,16.0

    The "16.0" value indicates support for v16. If it's not there, the mailbox doesn't support it.

  13. AMGT says:

    I've run the Exchange Activesync test under the Office 365 tab against my O365 mailbox.

    It gives confusing results:

    MS-Server-ActiveSync: 15.1

    MS-ASProtocolVersions: 2.0,2.1,2.5,12.0,12.1,14.0,14.1

    X-MS-RP: 2.0,2.1,2.5,12.0,12.1,14.0,14.1

    So which version do I have? 15.x or 14.x?

    On my iOS9 it behaves like 15.x because it shows Mail app features not enabled against my Ex2010 on prem serves.

    Please clarify.

  14. Adam the 32bit Aardvark says:

    Hi MaxM (and everyone else),

    To enable mobile access to shared and public folders on Exchange 2000 through 2013 (and soon 2016) you need a 3rd party tool such as CodeTwo Exchange Sync.

    The synchronization is not direct – first the application syncs the folder with a custom folder in the user's personal mailbox and the 2nd step is accomplished via EAS. More info on this page:…/synchronization-of-android-iphone-blackberry

    All the best,


  15. ivandretvic says:

    @Jason, Will the new EAS16 provide any control on using the email signature stored in Exchange Online/Exchange server?

    This would allow a standardised client on mobile devices, and a policy that can also be applied on the server to set the Exchange Server signature as preferred.

    Any feedback on this would be appreciated.


  16. ivandretvic says:

    @Jason, The protocols are now published and can be viewed here.…/cc307725(v=exchg.80).aspx

    The link above "preview documentation for EAS v16" is no longer valid.


  17. paulinux says:


    are there any news on clients that support v16 on android?



  18. Trapulo says:

    Icewarp supports shared calendars via ActiveSync. Just moved to O365, really I can't believe that Exchange doesn't.

    1. @Trapulo I just moved to Office 365 from Google Apps, Google Apps also support shared calendars over the Exchange Active Sync protocol on iOS devices.. I am also at a complete loss to why this is not supported by Microsoft!

  19. 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


  20. PennyB says:

    Im reviewing one of the possible changes with AS 16.0 now.  I have developers still developing with 14.1 that are communicating with an Exchange 2010 sp2 server and a Cloud Office 365 server.  We have a very specific issue with the conversion of an appointment to a meeting.  It works wonderfully for the Cloud Office 365 but the conversion is not properly completed on Exchange 2010.  I am trying to find out exactly what our issue is.   Is there any documentation on comparisons of the calendar updates to see if potentially we found one vs our developers coding just not being quite accurate?

  21. J C says:

    The account in O365 shows ver 16.0 , the user is running latest IOS and yet we don't see the drafts syncing in the outlook app or the default mail app on a IOS device.

    So is having EAS ver 16.0 supposed to work or not ? Exchange connectivity analyzer shows

    MS-Server-ActiveSync: 15.1

    MS-ASProtocolVersions: 2.0,2.1,2.5,12.0,12.1,14.0,14.1,16.0

  22. Aaron Cohoon says:

    Is there any list of known devices or client applications that are supported? So far I haven’t found any mobile device email clients that support two-way draft folder synchronization with EAS v16, although I’m sure this is something that will improve as the protocol is more widely adopted with the latest Exchange versions.

    Though not officially supported it’s been proven that one-way server-to-client draft sync was possible in certain earlier versions of ActiveSync. This was observed in the Mail app prior to iOS 8.1.2, and as recently as today for BlackBerry 10 devices. However, mailboxes that have been migrated from Exchange 2010 to Exchange 2013 or even 2016 lose this capability. I can only assume this is due to some change in the API required for the current protocol, but is there any article or doc to substantiate this?

  23. Please enable shared calendar support, or make shared calendars work as personal calendars in regards to active sync.. Not doing either is a serious design flaw.

  24. Peter says:

    Shared calendars????

    I’ve been using MS/ accounts just for calendars because they support shared calendars with full interaction on phones etc. This is the one thing stopping me move to 365.

  25. tjernagel says:

    Microsoft you are really funny…

    “Syncing the drafts folder was previously not supported. We’ve added that support in version 16. Now you can start an email on your EAS device and continue editing that draft back at your desktop by retrieving the mail from the drafts folder. Or, write your draft at your computer, then make the final tweaks and send it from your phone while you’re on the go.”

    This was available in 2010 and lost in 2013 and now your trying to make it look like your bringing us something new in 2016. No your not… You are putting us back in the position we were in 3-4 years ago.

  26. John Wright says:

    How in the world are shared calendars not added to EAS 16? This is on the top 10 most requested features of the uservoice site for the Outlook iOS/Android app, and the 10 ten user requested features of the Office365 Outlook uservoice site.

    Outlook OWA, Google Apps, Hotmail/, Yahoo, and Outlook for desktop have all had shared calendar support since 2010. Lack of shared calendars in EAS means NONE of the Exchange On-Premise or Office365 clients can have a company calendar available for editing on a mobile device.

  27. Glen R. Magistrado says:

    I thought syncing drafts from mobile apps to OWA is now supported?

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