Navigating Microsoft’s New Exchange Email Limits: How Retarus Offers a Scalable Solution for High-Volume Sending

23 April 2025

Share this article:

The Problem

Microsoft is implementing new tenant-level outbound email limits in Exchange Online, known as the Tenant External Recipient Rate Limit (TERRL).These limits aim to enhance service reliability and prevent misuse by capping the number of external recipients a tenant can email within a 24-hour sliding window.


Key Details of the New Outbound Email Limits

  • Definition: TERRL sets the maximum number of external recipients (those outside your tenant's accepted domains) a tenant can send emails to per day.
  • Trial Tenants: Capped at 5,000 external recipients per day, regardless of license count.​
  • Non-Trial Tenants: Limits are calculated using the formula:​  500 * (Number of Non-trial Email Licenses^0.7) + 9500 ​

This formula ensures that as the number of licenses increases, the allowable external recipients also increase, albeit at a decreasing rate per license.

For example:​

  • 1 license: 10,000 recipients​
  • 10 licenses: 12,006 recipients
  • 100 licenses: 22,059 recipients
  • 1,000 licenses: 72,446 recipients
  • 10,000 licenses: 324,979 recipients​
  • 100,000 licenses: 1,590,639 recipients​


  • Enforcement Schedule:
  • Worldwide (WW) Environment:
  • April 3, 2025: Tenants with ≤25 licenses
  • April 18, 2025: Additional tenants with ≤200 licenses
  • April 28, 2025: Additional tenants with ≤500 licenses
  • May 9, 2025: All remaining tenants
  • Government Community Cloud (GCC) Environment:
  • May 30, 2025: Report availability
  • June 30, 2025: Enforcement begins


Monitoring and Compliance

Administrators can monitor their tenant's email activity through the "Tenant Outbound External Recipients" report available in the Exchange Admin Center (EAC) under Reports > Mail flow. This report provides insights into current usage and helps ensure compliance with the new limits.


If a tenant exceeds its daily limit, subsequent emails to external recipients will be blocked, and senders will receive Non-Delivery Reports (NDRs) indicating the issue.


For more detailed information, please refer to the official Microsoft announcement: Introducing Exchange Online Tenant Outbound Email Limits.


A Solution

​In light of Microsoft's new outbound email limitations in Exchange Online, many organizations are seeking alternative solutions to maintain their email communication efficiency. Retarus Transactional Email emerges as a robust option, offering high-volume email delivery without the constraints imposed by Exchange Online.


Retarus Transactional Email: A Scalable Solution for High-Volume Email Needs

Retarus Transactional Email is designed to handle large volumes of emails, making it suitable for businesses that require reliable and scalable email delivery. Key features include:

  • Unlimited Recipient Capacity: Unlike Exchange Online, which imposes daily sending limits, Retarus allows sending emails to an unlimited number of recipients without restrictions.
  • High Throughput Rates: Retarus guarantees the ability to send up to 10 million emails per hour, ensuring timely delivery of transactional emails even during peak periods.
  • Flexible Integration Options: The service supports integration via REST API and SMTP, allowing seamless connection with various business applications and systems. ​
  • Advanced Deliverability and Reputation Management: Retarus employs sophisticated reputation management techniques, including CSA certification and dynamic IP routing, to maintain high inbox placement rates and sender scores.
  • Compliance and Security: With data centers in multiple regions, including the United States, Retarus ensures compliance with data protection regulations such as GDPR and HIPAA. ​


Implementing Retarus as a Complementary Solution

For organizations affected by Exchange Online's new sending limits, integrating Retarus Transactional Email can provide the necessary scalability and reliability for their email communications. By offloading high-volume transactional emails to Retarus, businesses can ensure uninterrupted delivery without overburdening their existing infrastructure.

 


The Leader in Information Logistics

As a provider that has been dedicated to email for more than 30 years, there are virtually no special features that Retarus is unfamiliar with. With flexible solutions and in-house support, Retarus can also cater to a company’s specific requirements, especially when it comes to deeper integrations, routing, or automation. Contact IDT to discuss how we can support you in enhancing your organization's email capabilities. 


Learn More about Enterprise Global Cloud Fax, Email and Secure Messaging Services.


Connect with Us: