Microsoft recently announced new tenant-level outbound email limits for Exchange Online. These limits, referred to as Tenant External Recipient Rate Limits (TERRL), regulate the number of emails that a tenant can send to external recipients per day. The limits are calculated based on the number of licensed email users within the tenant.
While most organizations will not be affected by these changes, businesses that rely on high-volume external email communication should take note. The rollout of these new limits begins in March 2025.
Key Changes: What’s New?
- The new Tenant External Recipient Rate Limit (TERRL) caps the number of emails a tenant can send to external recipients.
- The limit is calculated based on the number of Exchange Online or Exchange Online Protection licenses within a tenant.
- Microsoft will roll out the limits gradually throughout March 2025.
- A new report in the Exchange Admin Center (EAC) will show your tenant’s specific email limits.
- As soon as this report is available, I will link it here in this article.
Rollout Phases and Timeline
The new outbound email limits will be introduced in four phases:
| Phase | Date | Applicable to Tenants With |
|---|---|---|
| Phase 1 | March 3, 2025 | Up to 25 email licenses |
| Phase 2 | March 10, 2025 | Up to 200 email licenses |
| Phase 3 | March 17, 2025 | Up to 500 email licenses |
| Phase 4 | March 31, 2025 | All remaining tenants |
By the end of March 2025, all Exchange Online tenants will be subject to these new outbound email limitations.
How the New Outbound Email Limits Work
The maximum number of external recipients a tenant can email per day is calculated using this formula:
500 * (Purchased Email Licenses^0.7) + 9500
This means that tenants with more licenses can send more emails, but with diminishing returns per additional license.
Examples of Daily External Recipient Limits
| Number of Licenses | Max External Recipients Per Day |
| 1 | 10,000 |
| 10 | 12,006 |
| 100 | 22,059 |
| 1,000 | 72,446 |
| 10,000 | 324,979 |
| 100,000 | 1,590,639 |
For test tenants, the daily external recipient limit is capped at 5,000, regardless of the number of licenses.
What Happens if You Exceed the Limit?
If your organization exceeds the outbound email limit:
- External email delivery will be blocked. Additional emails to external recipients will fail.
- A non-delivery report (NDR) will be sent. Senders will receive an error message stating that the tenant has exceeded its daily email limit.
- Emails will be blocked until usage falls below the threshold. The block lasts until the rolling 24-hour window allows for additional emails to be sent.
What is a Rolling 24-Hour Window?
Unlike traditional daily limits that reset at midnight, this rolling 24-hour window continuously monitors outbound email volume.
- If a tenant reaches its external recipient limit at 2:00 PM, further external emails will be blocked.
- Emails will remain blocked until usage in the past 24 hours drops below the tenant’s limit.
- This could take anywhere from a few minutes to 24 hours, depending on sending patterns.
How to Prepare for the New Exchange Online Outbound Email Limits
- Check your tenant’s current email usage.
- Use the new report in the Exchange Admin Center (EAC) (available by the end of February 2025) to see how your organization is affected.
- As soon as this report is available, I will link it here in this article.
- Consider alternative email solutions.
- If your business sends large volumes of external emails, Microsoft recommends using Azure Communication Services Email instead of Exchange Online for mass email sending.
- Adjust email workflows.
- Businesses relying on high external email volumes may need to segment their email distribution lists or use dedicated bulk email services.
Conclusion
Microsoft’s new outbound email limits for Exchange Online are designed to improve security and email deliverability while reducing spam and abuse. Most organizations will not be impacted, but businesses that rely on high-volume external email communication should take proactive steps to adapt.
To stay ahead of these changes, check your Exchange Admin Center reports and consider alternative bulk email solutions if necessary.
For more details, visit Microsoft’s official announcement.
I will show you how to set up Azure Communication Services soon! Check out my Blog!
