Title: Some users’ outbound Exchange Online email messages may be marked as spam and not delivered
User impact: 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.
Current status: We’ve implemented multiple service optimizations to alleviate the impact experienced by this event, and anticipate these optimizations to take effect over the coming week. While we monitor service telemetry to determine the efficacy of the service optimizations in alleviating impact, we’re continuing to assess potential long-term solutions to fully resolve this issue.
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.
Start time: Thursday, April 11, 2024, at 6:30 PM UTC
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 update by: Wednesday, April 17, 2024, at 11:00 PM UTC
