Since the release of Exchange Server 2016 Cumulative Update 3 (CU3), which added support for installing Exchange 2016 onto Windows Server 2016 servers, there’s been a series of reports in support forums and blog comments about errors that customers are seeing.

Now Microsoft has acknowledged that there is in fact a known issue, and there is no current workaround for it.

If you attempt to run Microsoft Exchange 2016 CU3 on Windows Server 2016, you will experience errors in the IIS host process W3WP.exe. There is no workaround at this time. You should postpone deployment of Exchange 2016 CU3 on Windows Server 2016 until a supported fix is available.

That’s all the detail that has been publicly released by Microsoft at this time, but the guidance is clear. You should deploy Exchange 2016 only on Windows Server 2012 R2 until further notice.

Update: the Exchange team has added some more info:

There currently is no workaround for this problem. Exchange Server will install on Windows Server 2016 cleanly and appear healthy until the first reboot after creating/joining a DAG. Customers should avoid installing Exchange Server on Windows Server 2016 until a supported update for Windows Server 2016 is available. Customers whose production environment is impacted are encouraged to replace Windows Server 2016 with Windows Server 2012R2 if they cannot wait for the update.

Update 14/12/2016: an update has been released for Windows Server 2016 to resolve underlying issues that adversely impact Exchange 2016 servers.

About the Author

Paul Cunningham

Paul is a former Microsoft MVP for Office Apps and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul no longer writes for


  1. Shermaine

    I did install exchange 2016 CU12 on Windows 2016 std server, so far looks fine, but my server is on-prem server for the office365 cloud system, not doing much stuff

  2. M.R.M Rizmi

    I have a very strange issue in my one Exchange Server 2016 (out of three nodes) the MSExchange Transport Service is stop pending (it shows and cannot start). I had installed other two servers also in the same default settings based and there I do not have an issue. This is on Windows Server 2012 R2 Standard and fully patched and Exchange Server 2016 CU8. all receive connectors are default and I have no clue on resolving the same. Hence, seeking a support to rectify.

  3. Nadeem Muhammad Ali

    i am going to install Exchange Server 2016 CU8 on Windows Server 2016. Is it ok or still have some stability issues.

      1. Willstay

        Yes I read that but it is 2 years old. Hope Microsoft have fixed it by now.

  4. Jay

    What is the the latest update on this?

    Is it okay now to install Exchange 2016 CU6 to Windows Server 2016 Data center?

    I plan to build a standalone Exchange 2016.


  5. Joe

    I have a customer with 3 Exchange servers 2016 on Windows Server 2016. They all keep having troubles with updates and misc crashes/high CPU. There are no DAGS. We recently just introduced 3 new builds (same setup Exchange 2016 on Server 2016) and are finding those are exhibiting the same problem. Does anyone know if there ever was a permanent fix for this? I am thinking I may need to build 2012 R2 servers for Exchange 2016 for them, but dont want to do that if there really is a fix.

  6. Peter Nørredal

    Hi Paul
    Whats the status with installing Exchange 2016 CU7 on server 2016.
    Is it still not recommended ?

    I´m about to begin an exchange 2010 -> exchange 2016 migration – and would like to have some information about this issue before starting.


  7. Neal

    I’ve got Ex 2016 with CU4 and have just starting seeing this. No DAG but on 2012 R2 standard.

    Any Advise?

  8. Muhammad Usman

    I have recently installed exchange server 2016 on win 2016 servers. My environment is having i.e. domain/ dns with A.D. All is set up but when i try to send email from newly deployed exchange message stays in draft and says please try again later, we are still not ready. Can anyone support?


  9. Brian

    I didn’t see any updates released today that addresses this issue. Anyone else see anything? So I guess we wait another month.

    1. Avatar photo
      Paul Cunningham

      It’s not an Exchange patch. The issue was in the OS, and the Windows team has released an update to fix it.

      The Exchange team has noted it in their release announcement as well.

      “This update addresses the issue where IIS would crash after a DAG is formed and the server is subsequently restarted. This update is now required on all servers running Exchange Server 2016 on Windows Server 2016. Setup will not proceed unless the KB is installed.”

  10. Robert

    For all yours info, I’ve had a 2012R2 DAG setup with a reasonably small 650GB worth of mailstores. One of the nodes was acting up for a while up to the point that not a single Exchange update would install and to make matters worse, every Exchange update would crash out half way through and kill Exchange.
    So I thought it was time to move on. Yesterday I’ve installed Exchange 2016 CU3 on a Server 2016 node and so far that works fine, no IIS issues (apart from the obvious HTTPS/2 / cipher thing to be expected from Server 2016). I am running at a standalone node now though as I can’t create a DAG of 2012R2 and 2016. Today I was to install the second 2016 node and recreate the DAG. I might hold that down for a little while and make sure the backups run multiple times a day…

    What an annoyance again. I’ve run in so many issues with Server 2016 already, especially in the RDS field (start menu issues anyone?) that I really feel the OS just isn’t finished yet. The base OS is great, but it’s just not there yet.

    Thanks for the warning guys!

  11. Nick Sardelianos

    Damn, exactly what I needed – not.
    I may delay this for a month or so, but not more.
    I wonder if they can do anything in time.
    I won’t be using DAG, but still it scares me.

  12. Phil

    Thanks for this info! Wondered why I was getting those errors in my dev environment so often. Rebuilt my dev environment because of those errors. Unfortunately, I rebuilt it back onto Win Server 2016 again. Ha…. back to the drawing board. :/ Thanks Paul!

  13. DNash

    Do you know where we need to sign up to receive these official notifications from Microsoft? Thx for this timely notice.

    1. Avatar photo
      Paul Cunningham

      I wish I could tell you that there was one single source at Microsoft like an RSS feed or email list that reliably delivered this type of important announcement, but there isn’t.

  14. Phuong, Nguyen Van

    The best option deploy ex2016 on windows 2012R2.

  15. expta

    “No one deploys on-prem anymore” – PC

    1. Regulated

      Er… Ah… Ya they do… A lot… For a plethora of reasons.

  16. Gene

    Just installed server 2016 last night. Just found this article 2 minutes after starting install of Exch 2016 to be introduced in to Exch 2010 org.
    Thank you for stopping me in time!!

  17. Brian Lowery

    What if we are already in the middle of a 2010 to 2016 migration?

    1. Ron


      1. Ramy Othman


      1. Brian Lowery

        We installed Windows Server 2016 Standard. Its a planned stand alone server migrating out of a Small Business Server 2011 environment.

        1. Avatar photo
          Paul Cunningham

          The information from Microsoft so far is that there’s a bug and they recommend not continuing with deployments.

          Anecdotally, the issues seem to be occurring on database availability group members, and not on standalone servers. But that’s just an observation from reports and doesn’t guarantee that a standalone server won’t be impacted.

          If you continue, you take the risk that you’ll run into issues before a fix is available. Your other options are to halt and wait, or to move mailboxes back to the old server, then decom and rebuild the Exchange 2016 server on Windows Server 2012 R2 instead.

Leave a Reply