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Mailgun · Apps and SaaSSep 4, 2026, 12:20 UTC

Microsoft Incident Resulting in Delivery Issues to M365

InformationalNot disclosedUpdated 18h ago
Sep 4, 12:20 UTCSep 4, 12:54 UTC
Duration
34m
Impact
Informational
Root cause
Not disclosed
Mailgun, 90 days
11 incidents
Affected
Not listed by the vendor.
Status page

Final update

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

Timeline

  1. Resolved · Sep 4, 12:54 UTC
    Microsoft has resolved the underlying issue, we are seeing deliveries to M365 process normally.
  2. Monitoring · Sep 4, 12:22 UTC
    We are continuing to monitor for any further issues.
  3. Monitoring · Sep 4, 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.

More from Mailgun

Full history
StartedIncidentDuration
Sep 1409:15 UTCRoute delays in EU Region58m
Sep 414:16 UTCEU Messaging Outage17m
Aug 3114:47 UTCEvent Log Delays in US Region7h 14m
Aug 2720:38 UTCEU Messaging Outage37m
Aug 2016:19 UTCGCP Reporting Multi Service Outage in US-West11h 12m
Aug 1720:18 UTCEmail Delivery Failures to Microsoft 365 Domains0m

From vendors' own status pages and disclosures. Times as reported. Logos via logo.dev; trademarks belong to their owners.

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