UPDATED: Microsoft has released the Cumulative Update 4 for Exchange Server 2016 on December 13th, which addresses the issue described in the post below. You can find more details about the CU4 here

blog-exchange2016-windowsserver2016-bug_sqIf you are considering deploying the latest Exchange on the latest version of Windows Server, be aware there’s a major and yet unfixed bug.

Sometime the latest is not the greatest, and occasionally the “leading edge” becomes the “cutting edge” which quickly becomes the “bleeding edge” and that’s not good for anyone. While I am all for running out and trying the latest versions of any product Redmond produces, if you are considering deployment of Exchange 2016 on Windows Server 2016, stop.

And if you have already done this, like I did, and wondering why you keep having problems, you are not going crazy – there’s a bug. And it’s a pretty big bug, considering Server 2016 is the newest server operating system and Exchange 2016 is the latest version of the flagship Microsoft product, with the third cumulative update CU3 released on September 20th 2016 (build number 15.01.0544.027).

The bug exists between the CU3 version and IIS in Server 2016. When you install Exchange 2016 CU3 on to Windows Server 2016, or you upgrade an existing Exchange 2016 running on Server 2016 to CU3, you will encounter somewhat random but frequent crashes of the W3WP.exe process, which is the executable for IIS. Based on some independent reports, this issue doesn’t appear on standalone servers, but does on deployments with created database availability groups (DAG). And because IIS is affected, any HTTP-based protocols, like ActiveSync, OWA and remote PowerShell, experience issues.

The Exchange Team and the Windows Team are working extensively to run this bug down and stomp it out, but currently there is no fix either in the form of a readily downloadable update or even a custom fix. It’s a bug that, if you’re in the bad position of already being in this situation, requires you to uninstall CU3 at best, or even revert to Windows Server 2012 R2 if moving back to older Exchange versions is not an option. For those who haven’t done their upgrades or new installs yet, the best advice is to wait.

At present, there is no fix for this, and the latest guidance from Microsoft is to delay deploying Exchange Server 2016 to Windows Server 2016. An update will be forthcoming, and that may be as soon as December’s patch Tuesday next week. But until that patch is released, you really don’t want to go against Microsoft’s advice on this, particularly since it came direct from the Exchange team.

We will keep an eye out and post to the blog as soon as this issue has an available patch, and odds are good that we will see Exchange 2016 CU4 at the same time. If you are already running Exchange 2016 CU2 in Windows Server 2016, stay put for now. Nobody wants to run an unpatched server, but since CU2 is N-1, it’s still supported, and you can skip straight to CU4 when it appears.

Watch this space and GFI Software’s social media profiles for updates, as we’ll notify you as soon as we get an update on this. And if you’re by any case unsure which version you’re currently running and want to view the build number of the version of Exchange 2016 that you’re running, run the following command in the Exchange Management Shell:

Get-ExchangeServer | Format-List Name, Edition, AdminDisplayVersion