The issue has been resolved, and sending to Microsoft-owned domains has been restored.

We’re seeing delivery to Outlook.com, Hotmail.com, and other Microsoft-owned domains return to normal. Emails are now being delivered in a timely manner. We’ll continue to monitor closely.

We’ve identified that this issue is impacting domains in the eu-west-1 region. We’re actively escalating with Microsoft to resolve this as quickly as possible. Please reach out to support@resend.com for any questions and concerns.

We've identified that Microsoft addresses (outlook.⁠com, hotmail.⁠com, and other Microsoft-owned domains) are experiencing delivery delays at an elevated rate.

We've informed Microsoft and are monitoring.