New limits restrict any messages sent from onmicrosoft.com domains to 100 external recipients within a 24-hour period to curb spam. Spammers have been creating new Microsoft 365 tenants to send large volumes of unwanted email, harming the reputation of shared domains and impacting legitimate users. Organizations that exceed the limit will receive Non-Delivery Reports with error code 550 5.7.236. Internal mail and incoming messages remain unaffected. Companies using MOERA domains as primary addresses must purchase and migrate to custom branded domains. Sender Rewriting Scheme, Bookings invitations, and Microsoft product notifications may be impacted. Federated domains must add non-federated custom defaults.
Microsoft is introducing new limits for onmicrosoft.com domains. Organizations can now send a maximum of 100 external emails per day via these standard domains to prevent spam. The new measure limits messages from onmicrosoft.com domains to 100 external recipients within 24 hours. Previously, there were no limits for Microsoft Online Email Routing Address (MOERA) domains. Microsoft is responding to an ongoing issue within Microsoft 365. Spammers are abusing new tenants to send large amounts of unwanted emails before Microsoft can intervene.
Companies that currently use MOERA domains as their primary domain must take action. Microsoft recommends purchasing custom domains and migrating to them. Only branded domains should still be used for non-test email communication. The impact extends beyond standard email delivery. Sender Rewriting Scheme configurations, invitations from the Bookings app, and Microsoft product notifications may also be affected if they depend on MOERA domains. Organizations with federated domains will face additional complexity. They will need to add non-federated custom domains to serve as the default domain.
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