To prevent Exchange Online being used for high-volume emails to external recipients, Microsoft will be introducing additional rate limits from October 2025.
Why is Microsoft introducing this new rate limit?
Exchange Online does not support bulk or high-volume transactional email. Until now, Microsoft have not enforced the limiting of bulk email, but are doing so to help reduce unfair usage and the abuse of Exchange Online resources.
What is the new rate limit?
The limit will be 2,000 external recipients in a rolling 24-hour period. This is measured by recipient, not unique recipient, so sending multiple emails to the same external recipient will still count towards to the limit rather than just being counted once. Once the limit is reached, you will be blocked from sending to external recipients until the rolling total of emailed external recipients falls back below 2,000.
What other limits should I be aware of?
Exchange Online enforces a Recipient Rate limit of 10,000 recipients. This new 2,000 External Recipient Rate limit is a sub-limit within this overall 10,000 Recipient Rate limit.
How will the new rate limit be introduced?
- 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.
- Phase 2 – April 2026. The rate will start applying cloud-hosted mailboxes of existing tenants.
Are there any exemptions to this new limit?
Yes. There are currently two:
- Server-side synchronization – Used to integrate Exchange Online with Dynamics 365
- Outlook.com Power Platform – Connector – commonly used by Power Automate and Logic Apps
However, this may change in the future.
What if I need to send mass emails from a cloud mailbox?
Moving to Azure Communication Services for Email, which is designed specifically for high volume email sent to recipients external to your tenant, is the suggested alternative to sending directly via Exchange Online.
Summary
As there are many options for sending mass emails to external recipients, it is understandable that Microsoft wants to limit the use of Exchange Online for this purpose. Not only is it a drain on resources, but it can also negatively affect the reputation of the sending email addresses. If you are an existing Strategy 365 client and wish to discuss this new rate and your available options, get in touch with one of our experts today.
