Resolved on August 17, 2026, affecting Outbound Delivery.
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
Affected components
Update timeline
- resolved Aug 17, 2026, 08:18 PM 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
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