EX1224375: Exchange Online Service Health Incident (Service Restored)

[365 Service Alert]

Users routing their Exchange Online email through a third-party protection service may have send and receive delays.                                                                                                                                                                                        

Users routing their Exchange Online email through a third-party protection service may have send and receive delays ID: EX1224375 Issue type: Incident Status Service Restored Impacted services Exchange Online Details Title: Users routing their Exchange Online email through a third-party protection service may have send and receive delays User impact: 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. Final status: We've fully implemented our identified configuration change and confirmed using internal telemetry that it effectively mitigated this issue. We 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. Start time: Monday, January 26, 2026, at 6:00 AM UTC End time: Friday, January 30, 2026, at 6:25 PM UTC Root cause: Root cause: This issue was due to an issue with cache limit configuration that helps facilitate the impacts scenario process with SMTP mail flow. Next steps: - We're 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. This is the final update for the event. Is this message helpful? Did you find this email helpful? Yes No To customize what’s included in this email, who gets it, or to unsubscribe, set your Service health preferences. If you are receiving this email because your Admin added you as a recipient, please contact your Admin to unsubscribe. Privacy Statement Microsoft Corporation, One Microsoft Way, ​Redmond, WA 98052​