Email is a fundamental part of business communications. If your company uses Exchange Online to send transactional or application generated emails to outside recipients, then recent changes by Microsoft could significantly impact your business.
Microsoft has consistently made it clear that Outlook 365 / Online Exchange is not intended for sending bulk email to recipients who are external to an organization. Soon, they will start restricting these emails to stop abuse. It is important to understand these changes. You should also take immediate corrective action if this change will impact the deliverability of your legitimate emails.
Setting maximum limits
These new limits are commonly referred to as tenant external recipient rate limit (TERRL). They will restrict the number of external recipients that a tenant can email over a 24-hour period. The allowed number is based on a company’s purchased email licenses. It follows this formula:
- 500 × (Purchased Email Licenses^0.7) + 9,500
Note: Trial licenses have a set limit of 5,000 emails per 24-hour period.
Limit examples
- A company with 100 licenses would be allowed to send 22,059 emails over a sliding 24-hour time frame.
- With 500 licenses, they could send 48,247 emails.
- 72,446 emails for 1,000 licenses, etc.
Some emails are excluded from the count. Examples include:
- Journal archiving messages
- Automatic replies, such as Out of Office messages
- Notifications from Microsoft applications like SharePoint and Teams
- DSNs (delivery receipts, read receipts, non-delivery reports)
- Emails sent using Exchange Online high-volume email or Azure Communication Services
What happens when maximum limits are reached?
Based on the calculations above, if your organization hits its maximum 24-hour limit, all further emails will be blocked. This will result in a 550 SMTP response error code.
- Exceeding trial limit of 5000. 550 5.7.232 – Your message can’t be sent because your trial tenant has exceeded its daily external recipient limit.
- Exceeding calculated limit. 550 5.7.233 – Your message can’t be sent because your tenant has exceeded its daily external recipient limit.
Timeline for enforcement
The dates that these changes will be enforced are based on the number of tenant licenses. You should note that single license tenants and trial tenants are already being enforced.
Below are the key rollout dates as stated by Microsoft.
TERRL rollout schedule
|
Phase |
Enable enforcement for tenant group |
Rollout start date |
|
1 |
Tenants with <= 25 email licenses |
April 3, 2025 |
|
2 |
+ additional tenants with <= 200 licenses |
April 10, 2025 |
|
3 |
+ additional tenants with <= 500 licenses |
April 17, 2025 |
|
4 |
+ all remaining tenants |
May 1, 2025 |
Proofpoint can help
As Microsoft enforces these changes, it’s crucial to evaluate your strategies for sending outbound bulk email.
If you’re concerned about exceeding these limits, consider migrating to a next-generation solution like Proofpoint Secure Email Relay (SER). Proofpoint SER provides a robust, scalable alternative. SER can ensure that your email communications remain secure and uninterrupted.
Secure Email Relay is available standalone or as part of Proofpoint Prime, our comprehensive threat protection solution for stopping all human-centric threats. Prime empowers you to maximize your protection for both current and emerging threats while quickly realizing cost efficiency.
Learn more about Secure Email Relay or how Proofpoint Prime delivers security that meets the today’s security challenges. Visit the Secure Email Relay webpage or Prime Threat Protection webpage. Download our solution brief. Or contact a Proofpoint representative.
