Table of Contents
Summary
- Exchange Online is resuming enforcement of the Tenant External Recipient Rate Limit (TERRL) for tenants with more than 500 email licenses to prevent misuse and ensure service availability.
- The TERRL restricts the number of external recipients a tenant can email within a rolling 24-hour period; exceeding the limit results in blocked messages.
- Senders will receive a Non-Delivery Report (NDR) if the daily outbound external recipient limit is exceeded.
- Internal emails are not affected by this limit, but monitoring usage via the Exchange admin center is recommended.
- High-volume senders may need to consider alternative email services that do not utilize Exchange Online for outgoing messages.
Admin Impact: Medium
User Impact: Low
Release Start: 11 Mar 2026
Release End: 15 Apr 2026
Services: Exchange
Category: Plan for change
Tags: Admin Action
History
2/26/2026 Item Added to Message Center
Microsoft Message
As previously communicated in Message Center post MC101711, Exchange Online introduced a tenantlevel outbound email protection called the Tenant External Recipient Rate Limit (TERRL) to reduce misuse and abuse of the service and help ensure availability for all customers.
We temporarily postponed enforcement of this limit for tenants with more than 500 purchased email licenses. We’re now resuming the rollout and will begin enabling enforcement for these tenants in the coming weeks.
The TERRL limits the number of external recipients a tenant can send email to in a rolling 24hour period. If the limit is exceeded, additional messages sent to external recipients will be blocked until usage falls back below the quota.
A tenant’s daily quota is calculated based on the number of purchased email licenses using the following formula:
500 × (Purchased Email Licenses^0.7) + 9500
When will this happen
Enforcement for tenants with more than 500 email licenses will be enabled gradually in a staged rollout beginning mid-March 2026.
Start Date Number of Email Licenses
11-Mar 501–800
18-Mar 801–1,000
25-Mar 1,001–1,500
1-Apr 1,501–3,000
8-Apr 3,001–10,000
15-Apr 10,001+
How this will affect your organization
Once enforcement is enabled for your tenant:
- If your tenant exceeds its daily outbound external recipient limit, further messages to external recipients will be blocked until the rolling 24hour volume drops below the quota.
- Senders will receive the following NonDelivery Report (NDR):
- 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).
Internal mail and mail sent to internal recipients are not affected.
How to prepare
To help you plan and monitor usage, Exchange Online provides a dedicated report in the Exchange admin center:
EAC > Reports > Mail flow > Tenant Outbound External Recipients Rate
This report shows:
- Your tenant’s daily external recipient quota
- Current usage and percentage of quota consumed
- Any recipients blocked due to exceeding the limit
- Whether enforcement is currently enabled for your tenant
If your outbound volume is well below your quota, no action is required.
If your tenant regularly sends high-volume email to external recipients (for example, notifications or transactional messages), consider using and alternative bulk or high-volume email service that doesn’t route messages through your Exchange Online tenant.
For more information about the Tenant External Recipient Rate feature and report please see this blog post: Introducing Exchange Online Tenant Outbound Email Limits