Understanding the new Microsoft Exchange Online rate limits in 2025

In January 2025, Microsoft is implementing changes to the Exchange Online External Recipient Rate Limits, specifically targeting the number of external recipients users can send emails to in a 24-hour period. This new limit is set at 2,000 external recipients, significantly lower than what some organisations may be accustomed to. While designed to reduce spam and enhance security, this change will likely impact businesses that rely on Exchange Online for high-volume email communication.

What is changing?

The upcoming changes will cap the number of emails that can be sent to external recipients at 2,000 per user per 24 hours. This new rule is independent of the user’s subscription level or plan.

These updates are part of Microsoft’s effort to reduce spam and protect their email environment from being exploited. By lowering the threshold, Exchange Online aims to minimise the risk of large-scale spam campaigns or compromised accounts being used maliciously.

However, for legitimate users and organisations, this adjustment means rethinking their approach to large-scale email campaigns.

Example:
Consider a retail business sending daily promotional emails to a mailing list of 10,000 subscribers. Under the new rules, a single user could not send such emails directly from Exchange Online, as they would exceed the 2,000-recipient limit within just one campaign. This makes it necessary for businesses to explore alternative tools and strategies for bulk emailing.

A quick look at Exchange Online limits

Exchange Online has previously enforced certain limits on sending emails through their servers. These limits include:

• Message header size limit: The total size of all email header fields is 256 KB, with individual headers limited to 32 KB each.
• Subject length limit: Restricts the subject line to a maximum of 255 characters.
• File attachments limit: Allows up to 250 attachments per email, regardless of their total size.
• File attachment size limit: Sets the maximum size for a single attachment at 150 MB, though some email clients may enforce lower limits.
• Multipart message limit: Limits MIME (Mixed Internet Message-format) multipart messages to a maximum of 250 body parts or attachments.
• Embedded message depth limit: Caps the number of times an email can be forwarded in a single chain to 30 levels.
• Receiving limits: Set to 3,600 per hour, of which 33% can be from one sender.

With the new external recipient rate limit, Microsoft is adding another layer of control. While this helps enhance the platform’s integrity, it poses challenges for businesses that depend on email for large-scale external communication, such as marketing, customer service updates, and transactional notifications.

The impact on large-volume email senders

The 2000-recipient cap is particularly problematic for businesses and organisations that rely on large-scale external communications. If you’re wondering if you’d be affected by this change, consider whether you fall into any of these categories:

• eCommerce businesses: Retailers often send promotional campaigns, product updates, or shipping notifications to thousands of customers. For instance, a company running a Black Friday sale may need to quickly notify tens of thousands of customers. With the new limits, these campaigns could face delays if sent through Exchange Online.
• Educational institutions: Universities or schools frequently communicate with students, parents, and staff about updates, events, or announcements. Larger institutions may quickly exceed the recipient cap.
• Marketing agencies: Agencies managing campaigns for multiple clients often send high volumes of emails, such as newsletters or customer engagement emails, which can easily surpass the new limit.

Organisations that hit the cap may face significant delays, as emails beyond the limit will either be throttled or blocked until the 24-hour cycle resets. This could lead to missed opportunities, reduced customer satisfaction, and potential revenue loss.

Avoid being affected by these changes

While Microsoft’s new Exchange Online recipient rate limits aim to enhance security and system efficiency, they also pose challenges for organisations that rely on high-volume email communication. Businesses must adapt quickly to avoid disruptions. Spotler SendPro offers a practical and effective solution, ensuring seamless email delivery without compromising quality or compliance.