Microsoft to Temporarily Block Shared Hybrid App Use in Exchange on September 16

Microsoft has confirmed that it will begin the first temporary blockage of dedicated hybrid app use in Exchange environments on September 16, 2025. The decision follows the previously announced plan to phase out the shared service principal model for hybrid customers.

Microsoft said that the temporary blockage will last 48 hours, starting at 7 AM GMT on September 16 and ending at 7 AM GMT on September 18. And it applies globally across WW, GCC, GCC-H, DoD, and 21Vianet cloud environments.

So, who will face the disruption? Well, organizations that run both on-premises and Exchange Online user mailboxes. Besides, those who haven’t updated all on-premises Exchange Servers to April 2025 HU or later. Finally, if the dedicated Exchange hybrid app hasn’t been enabled yet, you’re on the list as well.

During the temporary block, users with on-premises mailboxes may lose access to free/busy lookups, MailTips, and profile picture sharing with Exchange Online accounts. Other core hybrid functionality, such as migrations, management, and mail flow, will remain unaffected.

With this announcement, Microsoft has also urged admins to set up the dedicated hybrid app before the enforcement window to avoid disruptions. Another enforcement is scheduled for October 7, 2025, ahead of the final deprecation of shared service principal use with EWS at the end of October 2025.