Microsoft 365 Alert – Service Degradation – Exchange Online – Some users’ email messages containing images may be incorrectly flagged as malware and quarantined – RESOLVED

26/08/2024 16:17:00 PM

NHSmail Reference: INC45257682

Microsoft Reference: EX873252

Issue Status: RESOLVED

Issue Description: Users’ email messages containing images may be incorrectly flagged as malware and quarantined.

More info: Emails sent after Monday, August 26, 2024, at 4:35 PM UTC were not impacted by this issue.

Final Update: 27/08/2024 08:57:00 AM –This issue has been resolved and telemetry indicates that over 99 percent of impacted emails have been unblocked and automatically replayed. Customers have also reported resolution, and Microsoft have confirmed that new emails are sending as expected.

Scope of impact: Impact is specific to some users who are served through the affected infrastructure.

Root cause: A recent change to our malware detection caused emails which contained a specific filetype signature to be incorrectly flagged as malware.

Next steps: For a more comprehensive list of next steps and actions, please refer to the Post Incident Report document.