Email Delivery Failures to Microsoft 365 Domains

Minor · Started Aug 17, 2026 · 1:18 PM

Duration

< 1m
Severity

Minor
Detection lead

—
User reports

—

Summary

Email Delivery Failures to Microsoft 365 Domains

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

Started

Aug 17, 2026 · 1:18 PM
Resolved

Aug 17, 2026 · 1:18 PM
Duration

< 1m
Severity

None

Event timeline

How this incident unfolded

✓

Resolved
Aug 17 · 1:18 PM Mailgun

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