New Tenant Outbound Email Limits for External Recipients in Exchange Online

Many organizations rely on email for bulk communication to external domains, whether for customer outreach, newsletters, or notifications. However, sending too many external emails too quickly can lead to deliverability issues, spam detection, or even domain blacklisting. To regulate email flow and prevent abuse, Microsoft introduced Tenant Outbound External Email Limits / Tenant External Recipient Rate Limit (TERRL)—a restriction on the number of external recipients a tenant can email within a 24-hour window.

Let’s dive into how this limit works and what it means for your email flow.

The Tenant External Recipient Rate Limit (TERRL) or tenant-level outbound email limits is the maximum number of external recipients a Microsoft 365 tenant can send emails to within a rolling 24-hour sliding window.

Who are considered as external recipients?

Anyone with an email address whose domain is not in your organization’s accepted domains is considered an external recipient. It includes personal email accounts (like Gmail or Yahoo) and even users from other Microsoft 365 tenants.

It works on a 24-hour sliding window. This means Microsoft tracks the number of external emails sent over the past 24 hours, not by calendar day.

Example:

• Your company can send up to 10,000 emails per day to external recipients.

• At 6:00 AM, you send an email to 6,000 people.

• At 3:00 PM, you send another email to 4,000 people.

• You’ve now reached the 10,000-email limit, so any more emails will be blocked. Microsoft keeps checking your past 24 hours of email activity.
• At 6:00 AM the next day, the tenant regains the quota and can be able to send up to 6,000 emails.

• After 3:00PM the next day, the remaining limit gets regained and now the tenant can be able to send 10,000 emails.

Below are the rollout phases for the Exchange Online Tenant outbound email limits enforcement.

Phase	Enable enforcement for tenant group	Rollout start date
1	Tenants with <= 25 email licenses	March 3, 2025
2	+ additional tenants with <= 200 licenses	March 10, 2025
3	+ additional tenants with <= 500 licenses	March 17, 2025
4	+ all remaining tenants	March 31, 2025

The Tenant External Recipient Rate Limit (TERRL) is determined by the number of email licenses purchased or if a tenant has only trial licenses.

Here’s how the limit applies:

• Trial tenants: Limited to 5,000 external recipients per day, regardless of license count.

• Non-trial tenants: The daily outbound limit is based on the number of purchased Exchange Online or Exchange Online Protection licenses. More licenses increase the limit, but each additional license adds fewer emails than the previous one.

TERRL Calculation Formula

Use the following formula to estimate your limit:

500 × (Purchased Email Licenses^0.7) + 9,500

Example Limits:

• 100 licenses → 22,059 recipients/day

• 1,000 licenses → 72,446 recipients/day

The following are not included in the TERRL quota:

• Journaling messages

• Automatic Replies (including Out of Office)

• DSNs (NDRs, Delivery Receipts, Read Receipts)

• Messages sent using Azure Communication Services email and Exchange Online High-volume Email offerings

• Email notifications from Microsoft cloud applications e.g. SharePoint, Teams, Yammer

Note: Emails between tenants in the same officially designated multitenant organization are considered internal.

If your tenant goes over its daily outbound email limit, any further emails to external recipients will be blocked, and senders will receive a Non-Delivery Receipt (NDR) with the following error:

• Trial tenants: 550 5.7.232 – Your message can’t be sent because your trial tenant has exceeded its daily external recipient limit.

• Non-trial tenants: 550 5.7.233 – Your message can’t be sent because your tenant has exceeded its daily external recipient limit.

For organizations that need to send emails beyond their limit, Azure Communication Services email is recommended for high-volume or bulk emailing.

Starting in late February, admins will have a new report to monitor outbound email usage in the Exchange Admin Center -> Reports -> Mail flow -> Tenant Outbound External Recipients Rate.

This report will display:

• The number of external recipients sent to.

• The tenant’s daily email limit and usage percentage.

• How many recipients were blocked due to exceeding the limit.

• Whether enforcement is enabled or disabled for your tenant.

You can also use the Get-LimitsEnforcementStatus cmdlet to retrieve information about your Tenant Outbound External Email Limits.

Note: To identify your top senders, you can use the “Top senders and recipients” report in the Microsoft Defender portal (Microsoft Defender > Email & collaboration reports > Top senders and recipients) or run a Message Trace in the Exchange Admin Center (EAC) for a detailed breakdown.

We hope this blog provided a clear overview of the new Tenant Outbound External Email Limits in Exchange Online. Feel free to drop your questions in the comments. Thanks for reading!