Upgrading to this new release is critical for continued support of Add-ins to be installed in Outlook in Microsoft Exchange Server 2016 or Exchange Server 2019. All new add-in manifest files will be signed with a new RFC3161-based timestamping, deprecating the use of SHA1-based timestamping. You will not be able to install and launch any new office add-ins until you upgrade to this new version.
How to get this update
To get this update, install one of the following updates:
Learn about the terminology that Microsoft uses to describe software updates.