By implementing the External Recipient Rate (ERR) limit, Microsoft is restricting the number of emails that a single user or mailbox can send to external recipients in 24 hours to 2,000.

If your business uses Exchange Online – Microsoft’s cloud-based email, calendar, contacts & task management service – this limit will apply to you. It applies to all email addresses outside of your organisation’s Microsoft 365 setup. This means that any email sent to someone outside of your business, for example customers, partners, or prospects, will count towards that 2,000 limit.

It’s worth noting that this new 2,000 external limit is a sub-limit to the existing 10,000 total recipient cap. So, if you send 2,000 external emails in 24 hours, you can send up to 8,000 internal emails within that same period. If you send 1,000 external emails, you have 9,000 emails at your disposal. Sending zero external emails in a day means you can send up to 10,000 internal emails and so on.

To avoid being caught out, it’s crucial to understand that the limit counts each recipient. Multiple emails to the same person all count towards the limit. So, for example, sending the same email to 100 customers will count as 100 recipients towards the limit. Sending 20 emails to the same 100 customers will count as 2,000 recipients.

The date that the External Recipient Rate limit will apply to you depends on whether you currently use Exchange Online.

Phase 1 – October 2025: For organisations (or ‘tenants’) new to Exchange Online and those trialling it, the ERR will apply from October 2025.

Phase 2 – April 2026: For businesses already using Exchange Online, the limit comes in from April 2026.

The short answer is anyone who sends emails via Exchange Online. If you do regular marketing email campaigns, send out newsletters or announcements to a big client base, or have multiple employees emailing the same contact lists, this change could impact you more than other businesses in the area.

Initially at least, Microsoft states there will be exceptions for some Microsoft integrations, including server-side synchronisation between customer engagement apps and email servers, as well as Outlook.com connectors.

The ERR limit pretty much does what it says on the tin: it limits the number of external emails you can send in any one day to 2,000.

If yours is a business that does minimal external communication via email, then the ERR limit is unlikely to significantly affect you.

However, If you rely on sending a lot of emails every day – and you don’t use a dedicated marketing automation platform to do it – you’re likely to be impacted. For example, if you’re in the tourism or hospitality industry and rely on regular email promotions. Or, perhaps you have a small sales team reliant on personalised outreach to potential new customers, who use their individual work email address to do it.

If you hit the limit, you’ll have to wait for 24 hours before you can send more external emails, delaying communications and disrupting daily operations.

If you have a legitimate need to send high volumes of external emails, now is the time to sort out a new solution outside of Exchange Online – like Azure Communication Services for Email.

We know that ‘new solutions’ can sound scary for local businesses, particularly if it’s an unexpected expense that’s not been budgeted for. We’re here to help, with no-nonsense guidance and cost-effective solutions you can trust.

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You can find out more about the ERR – including why Microsoft is implementing it – on the Exchange Team Blog.