Outage in Mailgun
Microsoft Incident Resulting in Delivery Issues to M365
Resolved MinorIncident Report
Summary AI Generated
A Microsoft-side incident beginning around 08:00 UTC caused elevated email deferrals across all M365 regions, with Mailgun receiving "451 4.7.500 Server busy" responses. Only M365 recipients were affected; no other email providers were impacted. Microsoft resolved the underlying issue within approximately 36 minutes, after which email delivery to M365 returned to normal.
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. No other email providers are currently affected.
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Latest Updates ( sorted recent to last )
RESOLVED
2 days ago - at 09/04/2026 12:54PM
Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.
MONITORING
2 days ago - at 09/04/2026 12:22PM
We are continuing to monitor for any further issues.
MONITORING
2 days ago - at 09/04/2026 12:20PM
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. No other email providers are currently affected.
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