The Exchange team at Microsoft have issued a warning to customers saying NOT to install .NET Framework 4.6.1 on Exchange servers.
We wanted to post a quick note to call out that since yesterday, the .NET Framework 4.6.1 has been made a recommended update on WU (Windows Update).
As we have already stated in the Exchange Supportability Matrix, at this time, this version of .NET framework is not supported by Exchange. In fact, we know of some issues if it is installed.
We are working with the .NET team to ensure that Exchange customers have a smooth transition to .NET Framework 4.6.1, but in the meantime, delay this particular .NET update on your Exchange servers (information on how this can be accomplished can be found in the KB article 3133990, How to temporarily block the installation of the .NET Framework 4.6.1).
Be careful when approving any updates within your WSUS server or deployment system ensurig you do not inadvertently approve the update for your Exchange servers.