If you have marketing, communications or sales departments that are using Exchange Online to “email blast” messages out to more than 2,000 recipients a day, you need to read the following:
In April 2024, we announced that Exchange Online would begin enforcing an external recipient rate limit (ERRL) of 2,000 recipients in 24 hours. This will begin in October 2025 at the earliest. (MC787382 – Exchange Online to introduce External Recipient Rate Limit)
Exchange Online currently enforces a Recipient Rate limit of 10,000 recipients. The 2,000 External Recipient Rate Limit (ERRL) will become a sub-limit within this 10,000 Recipient Rate limit. There is no change to the Recipient Rate limit, and both of these will be rolling limits for 24-hour windows. You can send to up to 2,000 external recipients in a 24-hour period, and if you max out the external recipient rate limit then you will still be able to send to up to 8,000 internal recipients in that same period. If you don’t send to any external recipients in a 24-hour period, you can send to up to 10,000 internal recipients.
This new limit is not going to be applicable to the following Microsoft integrations until further notice:
- Server-side synchronization between customer engagement apps and email servers
- Outlook.com – Connectors
How will this change happen?
The new “External Recipient Rate limit” will be introduced in 2 phases:
- Phase 1 – October 2025, the limit will apply to cloud-hosted mailboxes of trial tenants and all cloud-hosted mailboxes of tenants created after that date. This phase will include an Exchange Admin Center mail flow report detailing the External Recipient count of cloud-hosted mailboxes belonging to the tenant.
- Phase 2 – April 2026, we will start applying the limit to cloud-hosted mailboxes of existing tenants.
Please refer to the ACS email documentation (Prepare an email communication resource for Azure Communication Services – An Azure Communication Services concept article | Microsoft Learn) or reach out to your Microsoft account team for further support in this journey.
What are the options for customers who have business needs that exceed the ERR limit?
If you have a cloud-hosted mailbox that needs to exceed the ERR limit, you can move to Azure Communication Services for Email, which is designed specifically for high volume email sent to recipients external to your tenant.Is this limit counted against per recipient or per unique recipient?
We will be counting per recipient not per unique recipient. So, if you sent 100 emails to the same 5 external recipients, it would count as 500 external recipients.
Read more about this & remediation steps here:
(Note: This change only applies to Microsoft 365 Commercial instances. The rate limit will be applied to GCC instances in the future however at the moment, they are exempt.)
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