Microsoft 365 Alert – Service Degradation – Exchange Online – Users were unable to see conference room availability for Exchange Online through a room-booking application – RESOLVED

Announcements Arpan Das

14/07/2026 09:44:00 AM

NHS.net Connect Reference: INC46879051

Microsoft Reference: EX1427120

Issue Status: RESOLVED

Issue Description: Users were unable to see conference room availability for Exchange Online through a room-booking application.

More info: Affected users may have received HTTP 403 Forbidden errors when attempting to retrieve room mailbox availability data, which prevented meeting room availability lookups, booking, and scheduling operations.

Current Update: 15/07/2026 09:44:00 AM – Microsoft has completed the reversion of the aforementioned change and confirmed after an extended period of monitoring that impact has now been remediated.

Scope of impact: Impact was specific to some users attempting to see conference room availability for Exchange Online through the affected third-party room-booking application.

Root cause: A recently enabled service change affected how free/busy request tokens were processed, resulting in HTTP 403 errors when users attempted to retrieve conference room mailbox availability information.

Next Steps: Microsoft are reviewing their service change validation procedures to better identify similar issues during their development and testing cycles.