Microsoft has announced a significant update to Exchange Online, where the service limit for outbound emails are changed from a per-mailbox daily send limit to a new tenant-level outbound email limits.
The aim of this change is to enhance service reliability and prevent misuse of the shared resources.
Here’s a detailed overview of the update and its implications for Exchange Online users.
Overview of the Change
Based on the Receiving and sending limits from the Exchange Online limits a per-mailbox daily send limit, or Recipient Rate Limit (RRL) of 10.000 recipients per day has traditionally been enforced in Exchange Online.
However, to manage outbound email traffic and ensure fair usage, Microsoft will from April 2025 rollout the implementation of Tenant External Recipient Rate Limits (TERRL).
These new limits are calculated based on the number of Exchange Online and Exchange Online Protection licenses that a tenant have added, regardless of the number of assigned seats.
Basically, TERRL is the maximum number of external recipients that Exchange Online will allow a tenant to send messages to during the last day (24-hours sliding window).
External recipients are defined as recipients whose email address domains are not listed as accepted domain in the tenant.
The new maximum tenant external recipient rate limits:
- Tenants with only email trial licenses: Up to 5,000 total external recipients per day.
- Tenants with non-trial licenses: Outbound limit is based on the tenant’s email licenses, calculated from this formula:
500 * (Number of non-trial email licenses 0,7) + 9500
If the outbound sending limit is exceeded, Exchange Online will block subsequent messages to external recipients, and the senders receive one of these Non-Delivery Receipts (NDR):
- Trial tenants:
550 5.7.232 – Your message can’t be sent because your trial tenant has exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit) - Non-trial tenants:
550 5.7.233 – Your message can’t be sent because your tenant exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit)
Key Details
- Enforcement Timeline:
The rollout of the new TERRL quota will start from 03. April 2025 for tenants with a small number of licenses, and will gradually roll out to all remaining tenants from the end of April 2025.
Enforcement for tenants in the GCC environment will be enabled from 30. June 2025. - Impact on Users:
Microsoft expect that most Exchange Online customers will not be affected by the change. However, tenants that need to send more emails to external recipients than the new limit allows, are advised to use Azure Communication Services email for bulk or high-volume emailing to external recipients. This service is designed to handle high-volume email traffic efficiently and can help comply with the new limits. - New Reporting Tool:
A new report, Tenant Outbound External Recipients, has been available in the Exchange Admin Center (Reports -> Mail flow) since February 2025. This report can help organizations get an overview of their recent outbound mail flow statistics, and help administrators monitor their email usage to determine if they risk exceeding the TERRL limit.
Detailed Rollout Schedule
For tenants in the worldwide environment:
- Phase 1: Tenants with ≤ 25 email licenses – from 03. April 2025
- Phase 2: Tenants with 26 to 200 licenses – from 10. April 2025
- Phase 3: Tenants with 201 to 500 licenses – from 17. April 2025
- Phase 4: All remaining tenants – from 01. May 2025
For tenants in the GCC environment:
- EAC Report: Enabled from 30. May 2025
- Enforcement: Enabled from 30. June 2025
Messages not counted against the TERRL quota
Not all types of message for external recipients will be counted against the tenant TERRL quota. The following message types are excepted:
- Automatic Replies (including Out of Office)
- DSNs (NDRs, Delivery Receipts, Read Receipts)
- Journaling messages
- Messages sent using Azure Communication Services email and Exchange Online High-volume Email offerings.
- Email notifications from Microsoft cloud applications, including SharePoint, Teams, Yammer.
Conclusion
The introduction of the Tenant External Recipient Rate Limit presents a significant change by Microsoft to updated the outbound Recipient Rate Limit in Exchange Online to the new Tenant External Recipient Rate Limit or TERRL. By understanding and adapting to these new limits, organizations can continue to safely use the Exchange Online mail services while monitoring and adjusting to the new practice.
For more information and updates, please refer to the official Microsoft blog post here