# Mailgun: Microsoft Incident Resulting in Delivery Issues to M365

- Provider: [Mailgun](https://outages.cc/mailgun.md)
- Type: Incident
- State: Resolved
- Worst impact: Operational
- Started: 2026-09-04 12:20 UTC
- Resolved: 2026-09-04 12:54 UTC (lasted 34 min)
- Official update: https://stspg.io/bndrpj3pyg6b

## Updates from Mailgun

### resolved, 2026-09-04 12:54 UTC

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

### monitoring, 2026-09-04 12:22 UTC

We are continuing to monitor for any further issues.

### monitoring, 2026-09-04 12:20 UTC

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.