The Exchange product group released the September 2025 Hotfix Updates for Exchange Server SE, Exchange Server 2019, and Exchange Server 2016.
Hotfix updates do not contain security fixes, but address issues. They also might introduce or add support for functionality changes, such as dedicated Exchange hybrid app support.
Changes
The issue addressed in these hotfixes is:
Dedicated Exchange Hybrid Application
A gentle reminder that since the April 2025 security updates, Exchange hybrid supports the dedicated Exchange hybrid app. The dedicated Exchange hybrid app becomes mandatory in October 2025 for continued cross-premises functionality (free/busy, etc.). To make the required changes related to the Graph permissions model, you have some more time, as that will become required in October 2026. For more information, please visit this link.