# Microsoft Incident Resulting in Delivery Issues to M365

- Provider: [Mailgun](https://down.guide/mailgun)
- Level: confirmed
- Impact: Degraded
- lasted 34m
- started 2026-09-04 12:20 UTC
- id: DWN-e2c888448a
- Official page: https://stspg.io/bndrpj3pyg6b

## Updates from Mailgun
### 2026-09-04 12:20 UTC: monitoring
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.

### 2026-09-04 12:22 UTC: monitoring
We are continuing to monitor for any further issues.

### 2026-09-04 12:54 UTC: resolved
Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.

---
down.guide reads providers' official status pages every minute and adds its own evidence, always labeled. Free, no account. Agents: MCP at https://down.guide/mcp, REST at https://down.guide/api/v1, feeds at https://down.guide/feed. Built by Sazabi (https://sazabi.com/?utm_source=down-guide&utm_medium=markdown).