Microsoft 365 Alert – Service Degradation – Exchange Online – Users routing their Exchange Online email through a third-party protection service may have send and receive delays – RESOLVED

02/02/2026 08:40:00 AM

NHSmail Reference: INC46738563

Microsoft Reference: EX1224375

Issue Status: RESOLVED

Issue Description: Users’ Exchange Online email routed through a third-party protection service may have been delayed.

More info: This issue specifically impacted users who use Simple Mail Transfer Protocol (SMTP) as their Exchange Online connection method and routed their email messages through a specific third-party email protection service. The email delays, which impacted both sending and receiving email, occurred in all Exchange Online connection methods.

Current Update: 02/02/2026 08:40:00 AM – Microsoft has fully implemented their identified configuration change and confirmed using internal telemetry that it effectively mitigated this issue. They have determined that this issue was due to an issue with cache limit configuration that helps facilitate the impacts scenario process with SMTP mail flow.

Scope of impact: This problem may have impacted any user sending or receiving email messages when leveraging a specific third-party email protection service.

Next steps: Microsoft are continuing our research into identifying the root cause of this impacting event to better understand how to prevent it from happening again in the future.