Microsoft Throttles onmicrosoft.com Emails: Upgrade or Face Restrictions

Microsoft is warning companies using the onmicrosoft.com domain for emails to migrate to a custom domain or face email throttling. Starting October 15th, Microsoft will limit emails to 100 external recipients per organization per 24 hours, gradually expanding to all tenants by June 2026. This aims to combat spammers exploiting the onmicrosoft.com domain. Microsoft advises adding and setting a custom domain as primary to avoid restrictions, but migration might increase admin workload and necessitate credential updates.