Introducing Exchange Online Tenant Outbound Email Limits

UPDATE 3/3/2025: The rollout dates below have been updated.

As with all cloud services, Exchange Online imposes service limits to prevent misuse of Exchange Online resources and ensure availability for all users. For example, aside from the High-volume Email offering, Exchange Online doesn’t support bulk or high-volume email, yet until now we’ve mostly used only a per-mailbox daily send limit (known as the Recipient Rate Limit or RRL) to enforce this.

Going forward, we’re introducing new tenant-level outbound email limits (also known as the Tenant External Recipient Rate Limit or TERRL) that are calculated based on the number of email licenses a tenant has or if a tenant has only trial licenses. Enforcement for trial-only and single-seat tenants is already enabled. We’ll continue to enable enforcement for all other tenants in the Exchange Online multitenant standard environment in April, starting with tenants with a small number of licenses, then gradually including all tenants by May.

TERRL rollout schedule

Based on service telemetry, most Exchange Online customers won’t be impacted. A new report (Tenant Outbound External Recipients) will be made available in the EAC by late-February that will show your tenant’s limit. If your organization needs to send more email to external recipients than your limit allows, we recommend using Azure Communication Services email for bulk or high-volume emailing to external recipients.

More Information

The Tenant External Recipient Rate Limit (TERRL) is the maximum number of external recipients a tenant in good standing can send to per day (24-hour sliding window). External recipients are those whose email address domains are not an accepted domain in the tenant. The TERRL establishes base-line outbound sending limits for all tenants, but additional current and future restrictions can also occur due to factors like suspicious sending behavior, sending spam, fraudulent or excessively late payments, etc.

Below are the new maximum tenant external recipient rate limits:

• Trial tenants: Limited to 5,000 total external recipients per day, regardless of license count.
• Non-trial tenants: Daily outbound limit is based on the tenant’s email licenses (any Exchange Online or Exchange Online Protection license). More licenses increase the number of external recipients your tenant can send to per day, but at a decreasing rate per license. By late February you’ll find your tenant’s TERRL in the Tenant Outbound External Recipients report in the EAC Reports > Mail flow section. You can also use the following formula to determine your tenant’s TERRL:

500 * (Number of Non-trial Email Licenses^0.7) + 9500

Sample limits for tenants with various license counts are shown below:

If your tenant exceeds its daily outbound sending limit subsequent messages sent to external recipients will be blocked and senders will receive one of the following bounce messages (also known as Non-Delivery Receipts or NDRs):

• 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)

What is a “24-hour sliding window”?

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. Here’s an example of how this works:

Example: A single-seat tenant with 10k external recipients per day limit. Tenant sends two large messages to external recipients:

• Message 1, sent to 6K external recipients at 6:00AM on Day 1
• Message 2, sent to 4K external recipients at 3:00PM on Day 1

Illustration of TERRL 24-hour 'sliding window'

To help admins plan and track their outbound email volume, starting in late February you’ll find a new report in the Exchange admin center: EAC > Reports > Mail flow > Tenant Outbound External Recipients Rate. This report will show the current volume of external recipients, your tenant’s daily quota, how much of the quota is used, and the number of recipients that were blocked if the limit was exceeded. The report will also show if enforcement for the limit is enabled or disabled. For example, for tenants who have more than 500 email licenses it will show “Disabled” until May 1, the day we’ll start to enable enforcement for tenants who have more than 500 licenses.

Sample report in EAC

Frequently Asked Questions

What makes a recipient an “external recipient”?
Any recipient with a domain that is not an accepted domain in your tenant is considered an external recipient and when a message is sent to them it will count against your quota (exceptions to this are noted below). This includes messages sent to recipients in other Microsoft 365 tenants.

Note: Email sent to the sub-domain won't be automatically treated as Internal. There are two conditions where we will treat email sent to subdomain as Internal:

1. The subdomain is explicitly added as Accepted Domain.
2. The Root accepted domain has "Accept mail for all subdomains" option enabled. Remember, this is possible only when the root accepted domain type is Internal relay.

Will journaling or Out of Office messages count against this quota?
No. Several types of messages sent to external recipients from your tenant won’t get counted against your tenant’s TERRL quota, including the following:

• 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

What email licenses are used to calculate my tenant’s quota?
Licenses for, or that include, Exchange Online or Exchange Online Protection count towards the license count that is used to calculate your tenant’s quota.

Are the TERRL limitations based on the total number of email licenses (Exchange Online or EOP), or the total number of assigned licenses?
TERRL is based on the total number of email licenses.  For example, a tenant with 1000 licenses would be able to send 72,446 messages regardless of assigned seats (included non-licensed shared mailboxes).

Are messages to external recipients that are relayed through my tenant from my on-premises environment counted against the quota?
Yes. All messages sent outbound to external recipients from your tenant qualify for counting against your tenant’s quota, regardless of whether they originate from on-premises, from Exchange Online mailboxes, or from the Internet.

Are messages sent to my users’ on-premises mailboxes in an official Hybrid configuration counted against the quota?
So long as the mailboxes have email addresses that include an accepted domain in your tenant then these won’t count against your quota.

All my tenant’s email to internal Exchange Online mailboxes is sent out to a 3^rd party service for processing before it comes back into Exchange Online to be delivered to those internal recipients. Will these messages count against my quota?
No. If the recipient’s domain is an accepted domain in your tenant messages to them won’t get counted against the tenant external recipient rate limit, even if they are routed out then back into Exchange Online.

If I send a message to an external recipient but it routes out to a signature service or on-premises for processing, then comes back into Exchange Online to be sent out to the external recipient, will that get counted twice?
To reduce the risk of bad actors spoofing on-premises systems to send spam, we are currently counting these messages more than once. Our telemetry shows only a relatively small number of tenants are currently exceeding their quota, so it’s highly unlikely this will be an issue for your tenant. That said, we’re investigating alternative ways to prevent this type of spoofing that won’t double-count such messages.

Are cross-tenant messages within my multitenant organization treated as external messages?
No. While messages sent to other tenants hosted in Exchange Online are treated as external messages, messages sent between tenants within the same officially designated multitenant organization are treated as internal. See Plan for multitenant organizations in Microsoft 365 - Microsoft 365 Enterprise for more information on multitenant organizations in Microsoft 365.

If I send 1,000 messages to the same external recipient in a day does that count as 1 external recipient or 1,000 external recipients?
It counts as 1,000. The tenant external recipient rate limit doesn’t track unique external recipients.

If I send a message to a Distribution Group (DG) in my tenant that in turn has 1,000 external recipients on it will that get counted as 1 external recipient or 1,000 external recipients?
It counts as 1,000. The counting of external recipients happens after the DG (and its nested groups) is fully expanded to individual recipients.

Will outbound messages sent using the Exchange Online High-volume email (HVE) offering get counted against the TERRL quota?
No. HVE is primarily designed for sending high-volume email to internal recipients, not external recipients. That said, an HVE account does support sending to up to 2k external recipients per day. Messages sent to external recipients using HVE will not be counted against the TERRL quota. 

How can I identify the top senders in my tenant?
You can use the “Top senders and recipients” report in the Microsoft Defender portal (Microsoft Defender > Email & collaboration reports > Top senders and recipients) or use Message Trace in the EAC to aggregate a list of your top senders. We’re also considering adding a top senders list to the Tenant Outbound External Recipient Rate report later this year.

The report shows Enforcement is Disabled. What does that mean?
When Enforcement shows Disabled blocking is not happening, even if the report shows you’ve exceeded your quota, and it shows external recipients are getting blocked. The Disabled state will be shown during the initial rollout schedule for tenants for whom enforcement hasn’t yet been enabled (see the rollout schedule above). Once the feature is fully rolled out and enabled for all tenants by May, Enforcement will typically always show as Enabled and blocking will occur if the quota is exceeded.

Is there any type of notification or alert I’ll get when my outbound email volume exceeds my quota?
No, not at this time. We plan to add a system alert later this year that will notify admins when their outbound email volume exceeds 80% of the quota.

Will there be a cmdlet or Graph API to retrieve the data shown in the EAC report?
You can use the below Exchange Online PowerShell cmdlet to retrieve information about your Tenant External Recipient Rate Limit:

Get-LimitsEnforcementStatus

Sample output:

Verdict : Block
EnforcementEnabled: True
Threshold: 95980
ObservedValue: 243418

A Graph API is under consideration for a future update.

Microsoft 365 Messaging Team