Twilio outage on 2026-08-15: Widespread Microsoft 365 IP Block Causing Delivery Failures for Multiple Users

The incident is resolved and block rates are back to normal but customers will see change in block classifications from Microsoft 365. Users that continue to see elevated blocks can submit delisting requests to Microsoft by sending an email with a copy of the error message, and the blocked IP address, to "[email protected]". Delisting requests can also be made via the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com/