Mailgun: Microsoft Incident Resulting in Delivery Issues to M365
Timeline of updates
- 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.
- monitoring
We are continuing to monitor for any further issues.
- resolved
Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.
Archive proof
Rewindex commits each version of an incident it captures to a daily checkpoint, chains it to the day before, and has the checkpoint timestamped by FreeTSA and DigiCert. That proves this record existed by then and has not been changed since, by anyone, Rewindex included.
How the archive is checked, and what it cannot prove.
First version captured
In the 2026-10-17 checkpoint, timestamped by FreeTSA and DigiCert on . Record hash
281a34fa54f20928…
Impact, status and times are the vendor’s own, as last archived. View on stspg.io (opens in new tab).
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).
- Title
- Microsoft Incident Resulting in Delivery Issues to M365
- Vendor
- Mailgun
- Date
- URL
- https://rewindex.com/company/mailgun/incidents/cmp9x9s5n00g
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