Microsoft Investigates Exchange Online Bug Causing User Emails to be Incorrectly Quarantined

Microsoft is currently investigating a bug in Exchange Online that causes its spam protection systems to mistakenly quarantine emails from some users.

This incident has been categorized as a critical service issue and is being tracked under the reference number EX1038119 in the Microsoft 365 Admin Center.

According to Microsoft, «Certain URLs are being incorrectly classified and quarantined by our spam protection systems, resulting in unexpected consequences. Some Exchange Online users may find their emails unexpectedly quarantined.»

The company noted that «attempts to mitigate the issue by adding the affected URLs to the appropriate allow list have not been successful yet.» Specialists are working manually to rectify the locations of the impacted emails.

Engineers are also monitoring a separate incident (EX1038200) that is preventing users and administrators from accessing the «Overview» page in the «Email & Collaboration» section of the security portal.

Clients have reported similar issues over the past two days, including difficulties accessing the «Quarantine Overview» page while using Microsoft Defender for 365 to protect their emails.

In August 2024, Microsoft resolved a bug in Exchange Online that marked emails containing images as malicious and sent them to quarantine.

Recently, the company experienced an outage that blocked Outlook on the web users from accessing their Exchange Online mailboxes, as well as a bug that caused delays and issues in sending or receiving emails. Such outages have occurred several times in the last six months.