# Mailgun: Microsoft Incident Resulting in Delivery Issues to M365

> Mailgun status incident “Microsoft Incident Resulting in Delivery Issues to M365” on 2026-09-04: impact none (vendor’s label), 34 min, 3 update(s). Archived by Rewindex.

Canonical: https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g
Last updated: 2026-09-04T12:54:57Z

- Impact (vendor’s label): none
- Status: resolved
- Started: 2026-09-04 12:20 UTC · Resolved: 2026-09-04 12:54 UTC · Duration: 34 min
- Updates: 3
- [Vendor status page: https://stspg.io/bndrpj3pyg6b](https://stspg.io/bndrpj3pyg6b)
- [Company: Mailgun](https://rewindex.com/company/mailgun.md)

## Timeline of updates

- **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.
- **monitoring** 2026-09-04 12:22 UTC: We are continuing to monitor for any further issues.
- **resolved** 2026-09-04 12:54 UTC: Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.

## Cite this

Status incident (vendor impact label: none) posted by Mailgun, started 2026-09-04 12:20 UTC, resolved after 34 min, 3 update(s).

- Canonical URL: https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g
- Citation: Mailgun, “Microsoft Incident Resulting in Delivery Issues to M365” (2026-09-04 12:20 UTC). Archived by Rewindex: https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g (CC BY 4.0).
- Markdown link: `[Mailgun: Microsoft Incident Resulting in Delivery Issues to M365 (2026-09-04)](https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g)`


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Canonical: https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g · Markdown: https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g.md · JSON: https://rewindex.com/api/v1/companies/mailgun/incidents/cmp9x9s5n00g · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-11-05T17:24:29.165Z