Microsoft 365 Alert – Service Degradation – Exchange Online – Some users’ outbound Exchange Online email messages may be marked as spam and not delivered – RESOLVED

08/03/2024 09:02:00 AM

Microsoft Reference: EX719348

Issue Status: RESOLVED

Issue Description: Users’ outbound Exchange Online email messages may be marked as spam and not delivered.

More info: This isn’t connection method specific and thus occurs in all Exchange Online connection methods. Affected users receive a Non-Delivery Report (NDR) message that references the third-party anti-spam service name that has added the IP address to their block list.

Final Update: 25/04/2024 08:28:00 AM –  Microsoft have seen drastic improvements and significant reduction in the volume of impacted messages due to our implemented optimizations. They continue to proactively identify and stop spam messages through our ML antispam systems, as well as respond and implement further adjustments manually to block messages we manually find. Given that our optimizations have been successful, and because there’s no means to prevent all spam messages from ever occurring, they’re declaring this event resolved.

Scope of impact: The problem may impact some users sending outbound email messages if they’re leveraging a specific third-party anti-spam service mentioned within the NDR.

Root cause: A third-party anti-spam service is blocking a portion of Microsoft’s email IP address ranges to protect organizations that use their services.

Next steps: Microsoft are further working alongside the third-party anti-spam service to determine a proactive measure to identify Microsoft’s email IP address that are causing future impact and to implement optimizations before impact reoccurs on a broader scale.