Overview
- Users across Germany and other countries reported a sudden spike in problems with Outlook sign‑ins and the ability to send or receive mail on Monday evening, with outage trackers showing several hundred reports at the peak.
- Microsoft confirmed on its Microsoft 365 Status feed that customers experienced impairments to Exchange Online functions and that its teams are working to identify the root cause.
- One technical post suggested an expired certificate could be responsible but Microsoft has not confirmed a specific cause and continues its investigation.
- Some Exchange features such as calendar access were reported to be largely unaffected, and Microsoft advised users not to change local settings or repeatedly resend messages to avoid duplicate deliveries.
- Outage-aggregation sites like Downdetector and Allestörungen provided the first signals of scale and timing, and experts note certificate or authentication failures are a known recurring trigger for this type of cloud service disruption.