Microsoft is currently investigating a critical bug in Exchange Online that is causing legitimate emails to be incorrectly quarantined by anti-spam systems. The issue, which began at 10:11 UTC, is being tracked as incident EX1038119 in the Microsoft 365 Admin Center.

## Current Issues

According to Microsoft, “Specific URLs are being miscategorised and quarantined by our anti-spam systems, causing impact.” This is resulting in users’ Exchange Online email messages being unexpectedly sent to quarantine.

Microsoft’s initial attempts to resolve the problem by adding affected URLs to appropriate allow lists have been unsuccessful. Engineers are now working to manually correct affected email message locations while identifying additional problematic URLs.

## Additional Security Portal Problem

In a separate but related incident (EX1038200), users and administrators are unable to access the ‘Review’ page under the Email and Collaboration section in the Security portal. When attempting to access this page, users encounter a blank screen with no data loading.

Customers have reported similar issues over the past two days, including:
– Inability to access the Quarantine Review page in Microsoft Defender for 365
– Problems releasing quarantined emails

## Recent Exchange Online Problems

This is not the first email-related issue Microsoft has faced recently:
– In August 2024, Microsoft fixed a false positive issue where emails containing images were incorrectly tagged as malicious
– Earlier this week, an outage prevented Outlook on the web users from accessing their Exchange Online mailboxes
– A week-long Exchange Online outage recently caused delays and failures in sending or receiving emails

Microsoft continues to investigate the root causes of these issues while working on mitigation strategies.