Microsoft 365 Alert – Service Degradation – Microsoft Teams – Users are unable to communicate with external domains in Microsoft Teams – ONGOING

Announcements Arpan Das

16/04/2026 8:45:00 AM

NHSmail Reference: INC46801429

Microsoft Reference: TM1280599

Issue Status: ONGOING

Issue Description: Users are unable to communicate with external domains in Microsoft Teams.

More info: Users are unable to add external domain users to Teams group chats on both the desktop and web clients. Some users who were previously members of external domain group chats got removed from the chats.

Current Update: 16/04/2026 15:12:00 PM – Microsoft has applied a mitigation strategy to a portion of affected users to add previously removed external domain users back to their intended group chats and restore associated chat message history. In parallel, they are continuing to verify all impacted threads and ensure the mitigation is applied for all affected users.

Scope of impact: Your organization is affected by this event, and any user attempting to communicate with external domains in Microsoft Teams is impacted.

Root cause: Federation settings are being evaluated using the incorrect default setting as introduced by a recent service update, resulting in some federation connections being blocked despite the correct configuration.

Next update by: Thursday, April 16, 2026, at 9:00 PM UTC