MC1143991 | Limiting onmicrosoft domain usage for sending emails

Service

Exchange Online

Last Updated

2025-08-29T00:28:07.82Z

Published

2025-08-29T00:27:42Z

Message ID

MC1143991

Introduction To improve email deliverability and reduce abuse, Microsoft is introducing outbound email throttling for default MOERA domains (e.g., contoso.onmicrosoft.com). These domains are intended for initial tenant setup and testing—not for regular email traffic. This change encourages organizations to adopt custom domains with independent reputations. When this will happen General Availability (Worldwide): Rollout begins mid-October 2025 and will complete by early June 2026. Rollout timing will vary based on organization seat counts. For detailed rollout information, refer to Limiting Onmicrosoft Domain Usage for Sending Emails. How this affects your organization Organizations sending o...

Open Full Notification Browse Message Center

This page is an SEO landing page for discoverability of Message Center ID MC1143991.