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: While we continue to observe positive trends in certain IP address ranges, we’re actively assessing long-term solutions to effectively and permanently address 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.
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: Thursday, April 11, 2024, at 11:00 PM UTC
