DO NOT Install .NET Framework 4.7 on Exchange Servers

Thursday, May 18, 2017
Update 06/15/2017 - The Exchange Team updated their article to say that they are in the process of validating Exchange Server on the .NET Framework 4.7, but the work is not yet complete. They will update the Exchange supportability matrix when .NET Framework 4.7 is supported with certain versions of Exchange Server.
Update 06/13/2017 - The .NET Team published the article, How to temporarily block installation of the .NET Framework 4.7 using a registry key, similar to the one used to block previous versions of .NET. Exchange admins should implement this ASAP.

The Exchange Team also released the article, .NET Framework 4.7 and Exchange Server. It explains that .NET Framework 4.7 is not supported by any version of Exchange Server at this time, and how to remove it if you've already installed it.

Earlier this month the .NET Blog announced that the .NET Framework 4.7 has reached general availability. Do not install this update on your Exchange servers.

Refer to the Exchange Server Supportability Matrix which provides a central source for Microsoft Exchange administrators to easily locate information about the level of support available for any configuration or required component for supported versions of Microsoft Exchange. At this time no versions of Exchange Server support .NET 4.7, although this is subject to change with future cumulative updates. Exchange Server runs on .NET assemblies and changing to an unsupported version may have dire consequences.

According to the Q&A on the blog, .NET 4.7 is expected to be published to Windows Update in less than 3 months. That means without manual intervention you may wake up to find that Exchange is broken. When I asked, the .NET team said that they will provide a way to block .NET 4.7 installation via Windows Update using a registry key.

At this time, the registry key has not been made available. Check back on this blog post for any updates.

If you manually installed .NET 4.7, please refer to my earlier article, "How to Uninstall .NET Framework 4.6.1" for removal instructions. Those same instructions should work.

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