When you apply a cumulative update for Microsoft Exchange Server in a Microsoft Exchange Server 2016 environment, the Web.Config file for Outlook Web App is overwritten, and certain customized limits of the file must be reconfigured.


This issue occurs becauseĀ of a by-design behavior for all Exchange Server versions earlier than Exchange Server 2016 Cumulative Update 1.


To fix this issue, install Cumulative Update 1 or a later cumulative update for Exchange Server 2016.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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