Microsoft Partially Mitigates Week-Long Exchange Online Outage

A Prolonged Disruption in Email Services

Microsoft has addressed a week-long outage affecting Exchange Online, which caused delays and failures in sending and receiving emails. The disruption, classified as a critical service issue under EX1027675, impacted users worldwide. Many reported receiving Non-Delivery Reports (NDRs) with the error message “554 5.6.0 Corrupt message content.”

The issue first emerged on March 7 at 12:30 PM UTC, but Microsoft officially acknowledged it on March 10 at 11:14 AM UTC. The root cause was traced to a faulty service update intended to enhance message transport services. This update introduced a code issue that led to failures across portions of the Exchange Online infrastructure.

To mitigate the problem, Microsoft suggested that affected users send email attachments in ZIP format, as this workaround helped bypass the issue. By Wednesday morning, a fix was implemented, which helped resolve the initial outage.

However, a second, similar issue (EX1030895) emerged shortly after, causing additional email delivery failures. Microsoft acknowledged that this was affecting a smaller subset of messages, particularly those with winmail.dat attachments in plain text calendar invites. The company is now actively testing a fix on an isolated portion of its infrastructure, conducting targeted machine restarts, and monitoring diagnostic data to prevent further disruptions.

This recent incident follows a string of Microsoft 365 outages, including one affecting Outlook and Exchange Online authentication, as well as a Teams-related outage that disrupted call functionality. While Microsoft continues to address these recurring issues, customers remain frustrated by the frequency of service disruptions.

What Undercode Says:

Repeated Failures Raise Concerns Over Microsoft’s Service Stability
Microsoft’s Exchange Online and broader Microsoft 365 services have been plagued by multiple disruptions in recent months. While companies rely on cloud-based email for critical operations, these failures raise concerns about Microsoft’s ability to maintain service reliability.

2. The Risks of Faulty Updates

The root cause of this outage—a code issue introduced by a service update—highlights a major risk in cloud services: untested or insufficiently vetted updates. Microsoft’s struggle to fix the issue quickly suggests that their quality assurance (QA) process may need improvement.

3. Mitigation Strategies Need to Be More Transparent

Users were left to discover a workaround (sending ZIP attachments) on their own, as Microsoft’s guidance came after significant user complaints. A more proactive approach could have helped minimize frustration.

4. A Pattern of Microsoft 365 Service Degradations

From Outlook authentication failures to Teams call disruptions, Microsoft 365 users have faced multiple outages in quick succession. This suggests that Microsoft may be struggling with underlying infrastructure or software deployment issues that need urgent attention.

5. The Impact on Businesses

Enterprises and small businesses relying on Exchange Online faced delayed communications, lost productivity, and potential financial impacts. With no clear timeline for full resolution, Microsoft’s reputation as a reliable enterprise service provider is at stake.

6. Future-Proofing Cloud Services

For organizations relying on Microsoft 365, implementing failover strategies—such as secondary email services or on-premises backups—may become necessary to prevent complete disruption when Microsoft’s services fail.

7. Will Microsoft Learn from These Mistakes?

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Fact Checker Results:

✅ Microsoft confirmed that a service update caused the outage.
✅ The fix was deployed gradually, but some issues persist.
✅ A second issue (EX1030895) is still under investigation, with no full resolution yet.

References:

Reported By: https://www.bleepingcomputer.com/news/microsoft/week-long-exchange-online-outage-causes-email-failures-delays/
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