Posted on May 16, 2025.
Microsoft has announced a significant change to Exchange Online that could impact how organizations manage outbound email. Introducing the Tenant External Recipient Rate Limit (TERRL), a new tenant-level control that limits the number of external recipients a tenant can send emails to within a 24-hour sliding window.
What’s Changing in Exchange?
Historically, Microsoft enforced a per-mailbox daily send limit (Recipient Rate Limit). Starting now through June 2025, Microsoft has begun rolling out tenant-wide external recipient limits. These changes are designed to protect service health and reduce misuse, but they may catch some businesses off guard if they’re unaware or unprepared.
Rollout Dates for Worldwide Tenants:
- April 3, 2025: Tenants with ≤ 25 email licenses
- April 18, 2025: + tenants with ≤ 200 licenses
- April 28, 2025: + tenants with ≤ 500 licenses
- May 9, 2025: All remaining tenants
GCC Tenants:
- May 30, 2025: Reporting available
- June 30, 2025: Enforcement begins
Understanding the Tenant External Recipient Rate Limit (TERRL)
The TERRL is calculated based on your number of email licenses using this formula:
TERRL = 500 * (Number of Non-trial Email Licenses^0.7) + 9500
This formula ensures that the limit grows with your organization’s size, but not linearly, providing a balance between flexibility and protection.
For example:
- A tenant with 25 licenses = 14,259 external recipients/day
- 100 licenses = 22,060 external recipients/day
- 1,000 licenses = 72,446 external recipients/day
Trial tenants are capped at 5,000 external recipients per day, regardless of license count.
Why It Matters
If your organization relies on high-volume outbound emailing for client updates, notifications, or marketing, you could see legitimate mail blocked once your daily quota is reached. The result? Missed communications and frustrated users.
How Sanity Solutions Can Help
At Sanity Solutions, we specialize in helping businesses optimize and secure their Microsoft 365 environments. Here’s how we can support you:
- Assess Your Risk: We’ll help determine your current outbound usage and whether you’re likely to hit new TERRL limits.
- Monitor and Report: We’ll guide you through accessing the new Exchange Admin Center reports.
- Plan for Scale: If you’re approaching your limit, we’ll help you evaluate options.
- License Optimization: Ensure you’re maximizing the value of your existing email licenses or scaling smartly if your usage demands it.
Let’s make sure this change doesn’t disrupt your business. Reach out to Sanity Solutions today for a quick assessment or consultation.
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