Using classic Outlook for Windows in business environments
Thank you so much for contacting Microsoft Q&A Support.
Based on your description, it seems like your team is now limited to sending only 10 emails per hour due to Microsoft's recent rollout of new outbound email limits for Exchange Online tenants, known as the Tenant External Recipient Rate Limit (TERRL). During my research, I find that Microsoft introduced TERRL to reduce spam and abuse across its platform. This limit applies at the tenant level, not just per user and it is based on the number of email licenses your organization holds.
See more details in this: Introducing Exchange Online Tenant Outbound Email Limits | Microsoft Community Hub
I really appreciate that you've been a long-time Microsoft 365 customer. However, if your license counts maybe low or if Microsoft flags your sending behavior as potentially risky (e.g., bulk billing emails), your tenant may be throttled. Besides that, Microsoft is not targeting spam directly, but rather trying to prevent abuse at scale, which unfortunately can impact legitimate use cases like yours.
Thus, I try to find a possible workaround that it maybe helps you, please kindly consider doing this:
1.Check your current TERRL limit in the Exchange Admin Center (EAC) under the "Tenant Outbound External Recipients" report.
2.Consider increasing your license count if you're near the lower threshold.
3.For high-volume or bulk email needs (like billing), Microsoft recommends using Azure Communication Services Email instead of Exchange Online.
4.If this is a mistake or your usage is being misclassified, open a support ticket with Microsoft 365 Admin Center to request a review or exemption:
I hope this information can help you to fix this issue soon so that you can get back on track with your business.
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