To enhance security and maintain service availability, Microsoft is rolling out a new tenant-level outbound email limit for Exchange Online, known as the Tenant External Recipient Rate Limit (TERRL). This change impacts how many external recipients a tenant can send emails to per day and is set to take effect in phased stages starting in April 2025.
What is the Tenant External Recipient Rate Limit (TERRL)?
TERRL sets a daily limit on the number of external recipients a tenant can email. If a tenant exceeds this limit, further messages to external recipients will be blocked until the volume over the past 24 hours falls below the quota. The quota is determined by the following formula:
500 * (Purchased Email Licenses^0.7) + 9500
This means larger organizations with more licenses will have higher quotas, while smaller tenants will need to be mindful of their outbound email volume.
How is this Different from Existing Exchange Online Limits?
Previously, Microsoft imposed limits on outbound email at the individual mailbox level—such as restricting each user to 10,000 recipients per day. The new TERRL limit applies at the tenant level, meaning it caps the total number of unique external recipients across the entire organization, rather than per user. This change primarily affects businesses that send a high volume of external emails across multiple mailboxes.
Sample limits for tenants with various license counts are shown below:
| Number of Purchased Email Licenses | Tenant External Recipient Rate 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 |
Monitoring and Compliance
To help administrators track and manage outbound email volume, Microsoft is introducing a new reporting tool in the Exchange Admin Center (EAC):
EAC > Reports > Mail flow > Tenant Outbound External Recipients Rate
This report provides insights into:
- Your tenant’s daily external recipient quota
- Current usage percentage
- Number of recipients blocked (if the limit was exceeded)
- Whether enforcement is enabled or disabled
Rollout Schedule
TERRL enforcement will be phased in based on tenant size:
- April 3, 2025 – Tenants with ≤25 email licenses
- April 10, 2025 – Additional tenants with ≤200 licenses
- April 17, 2025 – Additional tenants with ≤500 licenses
- May 1, 2025 – Enforcement for all remaining tenants
What Happens if You Exceed the Limit?
If a tenant exceeds its daily external recipient quota, outgoing emails to external addresses will be blocked, and senders will receive a Non-Delivery Receipt (NDR) with error code 550 5.7.233 stating that the tenant has exceeded its daily limit.
What You Need to Do
- Review your usage – Check the new report in the EAC to determine your current outbound volume.
- Plan for high-volume needs – If your organization sends a significant number of external emails, consider using an alternative mass-mailing system or transactional e-mail system for your marketing emails which is not subject to TERRL quotas and is designed for high-volume external email communications.
For further details, refer to Microsoft’s official announcement: Introducing Exchange Online Tenant Outbound Email Limits.