Mailgun Status · History · Incident #62695

RESOLVED

Microsoft Incident Resulting in Delivery Issues to M365

Minor · Started Sep 4, 2026 · 5:20 AM

Duration

34m
Severity

Minor
Detection lead

—
User reports

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Summary

Microsoft Incident Resulting in Delivery Issues to M365

Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.

Started

Sep 4, 2026 · 5:20 AM
Resolved

Sep 4, 2026 · 5:54 AM
Duration

34m
Severity

None

Event timeline

How this incident unfolded

◉

Monitoring
Sep 4 · 5:20 AM Mailgun

Starting around 08:00 UTC, Microsoft began experiencing an incident causing an increased volume of deferred emails across all M365 regions. The affected responses are returning "451 4.7.500 Server busy". Our teams are actively monitoring the situation. Sending to other email providers is not affected.
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Monitoring
Sep 4 · 5:22 AM Mailgun

We are continuing to monitor for any further issues.
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Resolved
Sep 4 · 5:54 AM Mailgun

Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.

Pattern

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