Microsoft is investigating a major service incident inside Change On-line, recognized as EX1137017, which is stopping some customers from sending or receiving emails by the Outlook cell software.
The problem, which stays ongoing, particularly impacts clients using Hybrid Trendy Authentication (HMA), a standard configuration for organizations that combine on-premises Change servers with Change On-line.
The disruption has left affected cell customers unable to entry new messages or ship outbound mail from their gadgets, inflicting appreciable communication delays for these reliant on cell entry. The outage stems from a flawed construct replace just lately pushed to the manufacturing atmosphere.
Based on Microsoft’s preliminary root trigger evaluation, the brand new construct launched a crucial bug. When the system encounters a typical, non permanent community failure an occasion often dealt with gracefully it now generates an surprising exception for a subset of customers.
This exception improperly triggers a quarantine state for the mail synchronization job. Because of this, the method chargeable for syncing each inbound and outbound mail is suspended for a full 12-hour interval, successfully halting e-mail move to the person’s cell app.
Microsoft’s engineering groups have recognized the trigger and developed a repair. As of their final replace on Friday, August 22, 2025, at 8:50 AM, the deployment of this repair was in progress throughout the affected infrastructure.
The corporate acknowledged it’s actively monitoring the deployment’s saturation to make sure it resolves the problem with out introducing additional issues. Nonetheless, a definitive timeline for full decision has not but been supplied.
The scope of the influence is restricted to some customers on the Outlook cell app inside a hybrid atmosphere. Desktop and internet variations of Outlook don’t seem like affected by this particular incident.
This distinction highlights the mobile-centric nature of the bug, which targets the mail sync mechanism important for on-the-go system connectivity.
Directors and affected customers are suggested to observe the Microsoft 365 Service Well being Dashboard for updates concerning EX1137017.
Microsoft has dedicated to offering its subsequent main replace on the scenario by Monday, August 25, 2025, at 9:00 PM UTC, by which period they hope to have extra readability on the deployment’s progress and a timeline for full service restoration.
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