Mailgun outage, August 2026: Email Delivery Failures to Microsoft 365 Domains
Mailgun reported and resolved an incident: Email Delivery Failures to Microsoft 365 Domains. It lasted 1 minute.
OKResolved
From Mailgun's official status page, in their words.
What happened
- Started
- Resolved
- Duration
- 1 minute
- Impact
- none
- Affected
- Outbound Delivery
- Investigating
- Identifiednot posted
- Monitoringnot posted
- Resolved
Why it happened
Mailgun has not given a cause in its updates. We never guess one.
How it was resolved
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
Oldest first, from the first notice to the resolution. From Mailgun's official status page, in their words.
- resolved
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
What this means for a business (and what to check now)
- Retry anything that failed during the 1 minute.
- Enter any payments, bookings or jobs you took another way.
- If a deadline fell inside the window, keep this page as your record of the outage.
The full guide: what to do when a service you rely on is down
Other Mailgun incidents
- Route delays in EU Region, resolved after 1.1 hours
- Route delays in EU Region, resolved after 42 minutes
- Route delays in EU Region, resolved after 58 minutes
- EU Messaging Outage, resolved after 17 minutes
- Microsoft Incident Resulting in Delivery Issues to M365, resolved after 34 minutes
Hear about the next Mailgun incident as it starts
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