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Mailgun · Apps and SaaSAug 17, 2026, 20:18 UTC

Email Delivery Failures to Microsoft 365 Domains

InformationalNot disclosedUpdated 16h ago
Aug 17, 20:18 UTCAug 17, 20:18 UTC
Duration
0m
Impact
Informational
Root cause
Not disclosed
Mailgun, 90 days
11 incidents
Affected
Outbound DeliveryEmail Services - Outbound Delivery
Status page

Final update

We have received confirmation that an external issue impacting email delivery to Microsoft 365 domains has been resolved. Impacted messages would have received an error stating "5.7.511 Access denied, banned sender" between Friday, August 14th and Monday, August 17th. Any failed messages will need to be resent. Information on retrying messages can be found in our Help Center here: https://help.mailgun.com/hc/en-us/articles/18596982041883-Resending-messages

Timeline

  1. Resolved · Aug 17, 20:18 UTC
    We have received confirmation that an external issue impacting email delivery to Microsoft 365 domains has been resolved. Impacted messages would have received an error stating "5.7.511 Access denied, banned sender" between Friday, August 14th and Monday, August 17th. Any failed messages will need to be resent. Information on retrying messages can be found in our Help Center here: https://help.mailgun.com/hc/en-us/articles/18596982041883-Resending-messages

More from Mailgun

Full history
StartedIncidentDuration
Sep 1409:15 UTCRoute delays in EU Region58m
Sep 414:16 UTCEU Messaging Outage17m
Sep 412:20 UTCMicrosoft Incident Resulting in Delivery Issues to M36534m
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

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