Microsoft is rolling out a new policy in Exchange Online called the Tenant External Recipient Rate Limit (TERRL). This is a tenant-wide restriction that limits how many unique external email addresses a Microsoft 365 tenant can send to within a 24-hour period. The intent is to prevent abuse of the service and ensure consistent performance across all Microsoft customers.
This article outlines the TERRL policy, how it is calculated, when it is enforced, how to monitor it, and what happens if your tenant exceeds its limit.
What is TERRL?
The Tenant External Recipient Rate Limit (TERRL) is a cap on the total number of unique external recipients that can be emailed across your entire tenant within a 24-hour sliding window.
Key points
- External recipients are any email addresses not associated with your tenant’s accepted domains.
- The limit is tenant-wide, meaning it includes all messages sent from all users.
- This policy is separate from existing per-mailbox limits and is applied independently.
How is the Limit Calculated?
The daily external recipient limit for a tenant is calculated using the following formula:
500 * (number of non-trial email licenses ^ 0.7) + 9500Sample Limits by License Count
Number of Licenses | Daily External Recipient Limit |
|---|---|
1 | 10,000 |
2 | 10,312 |
10 | 12,006 |
25 | 14,259 |
100 | 22,059 |
1,000 | 72,446 |
10,000 | 324,979 |
100,000 | 1,590,639 |
Enforcement Timeline
Worldwide (WW) Tenants
Date | Applies To Tenants With… |
|---|---|
April 3, 2025 | 25 or fewer email licenses |
April 18, 2025 | 200 or fewer email licenses |
April 28, 2025 | 500 or fewer email licenses |
Government Community Cloud (GCC)
Date | Rollout Phase |
|---|---|
June 30, 2025 | Reporting available in EAC |
July 30, 2025 | Enforcement begins |
Additional government environments (GCCH, DoD, Gallatin) will follow in the second half of 2025.
Monitoring Your Usage
1. Exchange Admin Center (EAC)
Navigate to: Reports > Mail flow > Tenant Outbound External Recipients
Total external recipients in the past 24 hours
Your tenant’s current quota
Quota usage percentage
Number of recipients blocked if the limit was exceeded
Whether enforcement is enabled or disabled
2. PowerShell
Get-LimitsEnforcementStatusWhat Happens When You Exceed the Limit?
Messages to external recipients will be blocked.
Senders will receive a Non-Delivery Report (NDR).
NDR Codes
Trial tenants: 550 5.7.232 – Trial tenant exceeded its daily limit
Non-trial tenants: 550 5.7.233 – Tenant exceeded its daily limit
Email sending resumes automatically once usage drops below the limit.
What Doesn’t Count Toward TERRL?
Journaling messages created by Exchange Online rules
Automatic replies (e.g., Out of Office)
Delivery Status Notifications (e.g., NDRs, receipts)
Azure Communication Services messages
System-generated notifications from Microsoft apps (Teams, SharePoint, Yammer)
Exchange Online High-Volume Email solution messages
Recommendations for High-Volume Sending
If your organization sends bulk or transactional messages (marketing, alerts, notifications):
Avoid relying solely on Exchange Online mailboxes for this volume.
Use Azure Communication Services or other high-volume infrastructure.
Final Thoughts
TERRL is a strategic policy shift by Microsoft designed to reduce outbound abuse and promote consistent service quality. While it may require new planning and tooling for large-volume senders, it also provides transparent reporting and reliable enforcement.
Additional Resources:
Opensense Support
For further assistance, contact Opensense Support:
Email: help@opensense.com
Knowledge Base: help.opensense.com