Email Delivery Failures to Microsoft 365 Domains

Incident Report for mailgun

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

Posted Aug 17, 2026 - 13:18 PDT

This incident affected: Email Services (Outbound Delivery).