Exchange 2016 CU1 Released

Exchange 2016 CU1 has been released to the Microsoft download centre!  Exchange 2016 has a different servicing strategy than Exchange 2007/2010 and utilises Cumulative Updates (CUs) rather than the Rollup Updates (RU/UR) which were used previously.    CUs are a complete installation of Exchange 2016 and can be used to install a fresh server or to update a previously installed one. Exchange 2013 has the same servicing methodology. 


Exchange 2016 CU1 Download


This is build 15.01.0396.030 of Exchange 2016 and the update is helpfully named ExchangeServer2016-CU1.iso which allows us to easily identify the update.  Details for the release are contained in KB 3134844.

Exchange 2016 CU1 contains AD Schema changes.  

Update 17-3-2016 – Note that Exchange 2016 CU1 does not have the updated search service which can index of passive databases.  That will be scheduled for a future CU. 


Updates Of Particular Note

  • Exchange 2016 Cumulative Update 1 reverses the Mailbox Anchoring changes which were introduced in Exchange 2013 CU11.  These changes are outlined in the following blog article: Exchange Management Shell and Mailbox Anchoring.  And removal of the changes is discussed in this post
  • Updated OWA S/MIME control – a SHA2 certificate is now now used.  If a user has installed the old control, they must update to this new one. 
  • Exchange 2016 Cumulative Update 1 adds support for 17 additional languages in Outlook on the Web.
  • CU1 is distributed as an ISO file.  Did you notice the red underscore in the above screenshot?  ISOs can be easily mounted by double clicking them. 
  • There is an underlying issue with .NET Framework when Exchange is installed on Windows Server 2012 R2.  Only Exchange 2013 SP1 onwards are supported on Windows Server 2012 R2.  Whilst the .NET team works the issue, a workaround is to execute this on the Exchange server:

    “%windir%\Microsoft.NET\Framework64\v4.0.30319\ngen.exe update

    Errors and warnings encountered running this command can be safely ignored provided the final exit status code of 0 is reported in the output. 

  • Replay Lag Manager is enabled by default

  • Lagged database copy play down can be delayed based on disk latency, thereby ensuring active users are not impacted


Issues Resolved


Some Items For Consideration

Exchange 2016 CU1 follows the same servicing paradigm for Exchange 2013 which was previously discussed on the blog.  The CU1 package can be used to perform a new installation, or to upgrade an existing Exchange Server 2016 installation to CU1.  Cumulative Updates are well, cumulative.  What else can I say…

  • After you install this cumulative update package, you cannot uninstall the cumulative update package to revert to an earlier version of Exchange 2016. If you uninstall this cumulative update package, Exchange 2016 is removed from the server.

  • Ensure that you consult with all 3rd party vendors which exist as part of your messaging environment.  This includes archive, backup, mobility and management services.

  • Ensure that you do not forget to install this update on management servers, jump servers/workstations and application servers where the management tools were installed for an application.  FIM and 3rd party user provisioning solutions are examples of the latter.

  • Ensure that the Windows PowerShell Script Execution Policy is set to “Unrestricted” on the server being upgraded or installed.  See KB981474

  • Disable file system antivirus prior to installing.

  • Once server has been restarted, re-enable file system antivirus.

  • Note that customised configuration files are overwritten on installation.  Make sure you have any changes fully documented!

  • CU1 contains AD Schema updates for your organisation – please test and plan accordingly! 


Please enjoy the update responsibly!

What do I mean by that?  Well, you need to ensure that you are fully informed about the caveats with the CU  and are aware of all of the changes that it will make within your environment.  Additionally you will need to test the CU your lab which is representative of your production environment.



Comments (9)

  1. David Guillaume says:

    Hi Guy’s

    couple of questions;

    1. Is an exe version available?
    2. why is it so large compared with the first release –



    1. Hi David,

      The download is ISO only.

      The previous releases are compressed self extracting .exe files. I just expanded Exchange 2016 RTM to disk, and when extracted that is 5.5GB. So the CU1 ISO size is slightly larger than that.

      I used to have to download, extract and use a 3rd party utility to turn the extracted folder to a .ISO to mount into my VMs. So I do save that time and effort, but do appreciate the point that the initial download is larger.

      Zipping the Exchange 2016 CU1 ISO, using Windows 10’s native compression takes it down to ~2.2GB.



    Is the update safe? Has anyone ran into any problems?

  3. rob carsey says:

    Super cool that CU1 is finally out. However, after upgrading, I get 404 errors when going to either OWA or ECP. I believe the problem is that I’m using ADFS authentication. If I turn ADFS authentication off and use forms-based authentication, things seem to work OK. If I turn ADFS authentication back on. 404. The error occurs after authenticating with the ADFS server…after I get sent back to Exchange.

    Still trying to google my way out of this problem before opening a support call.

  4. Jeff Belt says:

    Hi, I’m also getting the 404 error (and a 500 error on ECP) and we use ADFS Auth. I’ve tried it on two servers with the same outcome, so darn’t update our other 3.

    If I switch it to forms auth it starts working, and if it proxies to an EX2010 mailbox it also works.

    Have you managed to get it resolved yet?


    Jeff Belt
    Teesside University

    1. Eric Masse says:

      I’ve just upgraded to Exchange 2016 CU1 and I’m also experiencing the “500 – Internal server error” when accessing ECP. I’m also authenticating using ADFS.



  5. Hi folks,

    Have you called in to create a case on this? We’ll need that for tracking purposes.


  6. Wajeeh says:

    Dear All,

    The problem of error 500 in ECP/OWA on 2016 after CU1 is addressed or not?

    1. Frank Buchholz says:

      We had the same issue after update the system with CU1. Are they a solution or fix available?
      We checked the google search for that issue, but it seams to be valid.

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