Exchange Online Introduces New Tenant Outbound Email Limits – How It Affects Your Organization

Microsoft has rolled out new tenant-level outbound email limits, known as the Tenant External Recipient Rate Limit (TERRL), for Exchange Online customers. This update is part of a broader plan to enforce external recipient rate (ERR) limits for individual mailboxes starting in October 2025.

In Exchange Online, Tenant External Recipient Rate Limit (TERRL) is a policy that limits the number of emails a tenant can send to external recipients within 24 hours. External recipients are those whose email addresses are outside the tenant’s accepted domains.

According to Microsoft, the new limits will be determined by the number of email licenses an organization has purchased. However, the limits are calculated differently for organizations with trial licenses. Microsoft has already enforced these limits for organizations with only trial licenses or a single email license.

“Daily outbound email volume and quota are tracked using a 24-hour sliding window. If you exceed your limit, subsequent outbound messages will be blocked until your volume of external recipients from the last 24 hours drops below the limit. This could take minutes or up to 24 hours, depending on your email sending pattern,” the Exchange team explained.

How Exchange Online outbound email limits differ by license type

Microsoft stated that organizations with trial licenses can send emails to up to 5,000 external recipients within 24 hours. Meanwhile, for customers with purchased email licenses (Exchange Online or Exchange Online Protection), the daily outbound email limit depends on the number of subscriptions they have.

Administrators can calculate their tenant’s TERRL using the formula: 500 × (Purchased Email Licenses^0.7) + 9,500. For example, an organization with 100,000 Exchange licenses would have a daily limit of 1,590,639 external recipients. If this limit is exceeded, any additional outbound emails to external recipients will be blocked, and senders will receive bounce messages as a notification.

Starting in March, Microsoft will begin enforcing these limits for all remaining tenants in the Exchange Online multitenant standard environment. The rollout will begin with organizations that have fewer licenses and gradually extend to all tenants by April 2025.

Microsoft reiterated that customers shouldn’t send large volumes of email through standard mailboxes. The company recommends using Azure Communication Services email for managing bulk or high-volume emailing to external recipients. Alternatively, organizations can use third-party email solutions to handle external traffic.

Microsoft adds new EAC reports

Microsoft has introduced a new report that lets administrators plan and track their outbound email volume in the Exchange admin center. They can access this report by heading to EAC > Reports > Mail flow > Tenant Outbound External Recipients Rate. This report will show the number of external recipients that have received emails, the daily quota of the tenant, quota usage, as well as the number of blocked recipients if the limit was exceeded.

The new EAC reports also help to track whether the limit enforcement is currently enabled or disabled. Additionally, administrators can use the Get-LimitsEnforcementStatus through the Exchange Online management module to retrieve information about the Tenant’s External Recipient Rate Limit.