Microsoft Incident Resulting in Delivery Issues to M365

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

• ◉

  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.

• ◉

  Monitoring

  Sep 4 · 5:22 AM Mailgun

  We are continuing to monitor for any further issues.

• ✓

  Resolved

  Sep 4 · 5:54 AM Mailgun

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