Microsoft 365 Alert – Service Degradation – Exchange Online – Users may experience delays sending and receiving email messages from external domains in Exchange Online – RESOLVED

07/09/2026 04:58:00 PM

NHS.net Connect Reference: INC46927021

Microsoft Reference: EX1467029

Issue Status: RESOLVED

Issue Description: Users may have experienced a delay in sending and receiving email messages from external domains in Exchange Online.

More info: Users may have experienced intermittent “Server busy” errors, affecting multiple mailboxes.
Depending on the client, the service should attempt to periodically retry sending the email previously impacted by the issue. If the initial sender received an NDR after 24-72 hours (different clients or email providers can vary), they will need to send a new email.

Final Update: 07/09/2026 04:59:00 PM – Microsoft has confirmed that the issue is resolved after an extended period of monitoring and receiving additional confirmations from previously impacted organisations.

Scope of impact: This issue impacted users who may have been attempting to send and receive email messages from external domains in Exchange Online.

Root cause: The enforcement of a specific anti-spam model contributed to impact for a subset of email traffic. They will provide more details within the Post-Incident Report.

Next steps: Microsoft is reviewing model classifications, rule configurations and upstream data pipelines to determine why the anti-spam model started to impact a subset of email traffic.

They will provide a preliminary Post-Incident Report within two business days and a final Post-Incident Report within five business days.