Organizations increasingly rely on automated email communications from platforms such as Oracle EBS and Oracle Fusion Cloud for essential business processes. Recent updates and forthcoming to Exchange Online introduce new outbound email limitations, specifically the Mailbox External Recipient Rate Limit (ERR, MERRL) and the Tenant External Recipient Rate Limit (TERRL), more generally just External Recipient Rate Limit (ERRL).
As highlighted in the STR Software blog post “Solving Microsoft 365 Rate Limits when Sending from Oracle EBS and Oracle Fusion Cloud,” these limits can pose significant challenges for entities that generate high volumes of automated emails. This post aims to provide Oracle EBS and Fusion Cloud users with a comprehensive understanding of these evolving restrictions and to outline practical strategies for managing their automated email sending to maintain operational continuity.
Understanding the New Microsoft 365 Recipient Rate Limits: What Oracle Users Need to Know
Microsoft has implemented new measures to manage the usage and prevent abuse of Exchange Online resources, impacting how organizations send email, particularly to external recipients.
| Per-Mailbox External Recipient Rate Limit (MERRL) | Tenant External Recipient Rate Limit (TERRL) | |
| Timing of Enforcement | April 2026 for existing tenants, October 2025 for new tenants | Starting in April 2025 (rolling) |
| Sending Limit | 2,000 external recipients (sub-limit of 10,000 total recipients)
*Per External Email, Not Unique Recipient* | Tenant-wide limit based on the number of email licenses. Example 1: 1,000 mailboxes = 72,446 external recipients Example 2: 10,000 mailboxes = 324,979 external recipients *Per External Email, Not Unique Recipient* |
The (Per-)Mailbox External Recipient Rate Limit (MERRL)
Beginning in October 2025 for new tenants and April 2026 for existing tenants, Exchange Online will enforce an external recipient rate limit of 2,000 recipients within a 24-hour period for each cloud-hosted mailbox. This ERR limit is applied per user/mailbox. It functions as a sub-limit within the existing 10,000 total recipient rate limit. This means that even if a user reaches the 2,000 external recipient limit, they can still send to up to 8,000 internal recipients within the same 24-hour window. Conversely, if no external recipients are contacted, a user can send to up to 10,000 internal recipients.
External Recipient Limit
The Tenant External Recipient Rate Limit (TERRL)
In addition to the per-mailbox limit, Microsoft is introducing a tenant-wide daily limit on the total number of external recipients all mailboxes within a tenant can send to. Enforcement of this TERRL began in April 2025 and is being rolled out in phases. The TERRL is primarily calculated based on the total number of email licenses (including Exchange Online or Exchange Online Protection licenses) held by the tenant. The limit increases with the number of licenses, although at a decreasing rate per license.
Why These Limits Matter for Automated System-Generated Emails
Automated systems originating from Oracle EBS and Oracle Cloud often generate and send significant volumes of emails for various business-critical functions, such as invoicing, purchase orders, and system notifications. These systems frequently communicate with external partners, customers, and vendors, making them susceptible to exceeding both the per-mailbox MERRL and the tenant-wide TERRL.
The new limits are specifically intended to manage and control bulk and high-volume transactional email, aligning with many automated systems’ typical output. Therefore, Oracle users must be particularly aware of these changes and their potential impact on automated communication workflows.
Impact on Email Flow Architecture for Oracle EBS and Cloud Integrations
Understanding how Oracle systems integrate with and relay emails through Microsoft 365 is crucial for anticipating the impact of these new limits.
Common Email Flow Scenarios
A typical architecture involves Oracle EBS or Oracle Cloud systems relaying emails through Microsoft 365 using SMTP relay or similar mechanisms. In such configurations, even though the emails are generated outside of Exchange Online mailboxes, they still traverse the Microsoft 365 tenant infrastructure when being sent to external recipients. Consequently, these outbound messages are subject to the tenant’s ERR (if a specific mailbox is used for sending) and, critically, the overall TERRL.
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Potential Bottlenecks and Challenges
Hitting the Limit
The introduction of the MERRL means that all messages sent outbound to external recipients from a mailbox count against the mailbox’s quota. This includes individual senders, including shared mailboxes and mail-enabled groups (as an example, this can include email addresses such as “accounting”@domain.com and “donotreply”@domain.com).
While, the introduction of TERRL means that all messages sent outbound to external recipients from the tenant are counted against the quota.
These limits are applicable regardless of whether they originate from Exchange Online mailboxes directly, on-premises systems like Oracle EBS, or internet-connected applications like Oracle Fusion Cloud. If automated Oracle systems generate a high volume of external emails, the tenant is at risk of exceeding its daily sending limit.
If these limits or quotas are hit, emails will be blocked from sending and your senders (mailboxes) will receive Non-Delivery Receipts (NDRs) with the error code 550 5.7.233. This disruption can severely impact the timely delivery of crucial business documents.
Double-Counting
Furthermore, there is a potential risk of double-counting external-bound emails if they are routed out of Exchange Online for processing by third-party services (e.g., email signature or archiving solutions) and then routed back into Exchange Online before being sent to the final external recipient. While Microsoft acknowledges this and is investigating alternatives, it currently advises that such messages might be counted more than once against the ERRLs.
Other Considerations
It is also important to reiterate that Exchange Online is not designed to accommodate bulk-mailing scenarios. Relying solely on Exchange Online for high-volume automated emails from Oracle systems can inherently lead to these rate limitations being encountered.
Finally, misconfigurations in hybrid environments, such as certificate mismatches with on-premises gateways, can sometimes lead to external emails being incorrectly attributed to the sending tenant and thus counted against the ERRLs.
Strategies for Oracle Users to Navigate Microsoft 365 Email Limits
Proactive planning and adopting appropriate strategies are essential for Oracle EBS and Cloud users to manage the new Microsoft 365 email-sending limits effectively.
Optimizing Email Sending from Oracle Systems
- Implement batching and scheduling: Configure Oracle systems to send automated emails in batches and schedule them throughout the day to avoid large, sudden spikes in outbound volume.
- Prioritize critical communications: Identify essential automated emails and potentially delay sending less time-sensitive notifications.
- Implement monitoring and alerting: Establish mechanisms to track the volume of outbound emails from Oracle systems to proactively monitor usage against the MERRL and TERRL.
- Review and optimize email frequency: Evaluate the necessity and frequency of automated reports and notifications sent to external recipients.
- Consolidate notifications: Where feasible, consolidate multiple individual notifications into a single, more comprehensive communication to reduce the overall number of external emails.
Consider Alternatives
Consider utilizing Oracle add-ons designed to handle large-volume bulk sending. STR Software’s AventX is designed to provide a comprehensive document and report delivery solution for Oracle EBS and Oracle Fusion Cloud. One of the solution’s many benefits is the ability to send your email off of Microsoft 365, bypassing the rate limits for high-volume senders and offering more reliable delivery of critical business documents from Oracle systems.
Additionally, AventX provides advanced features such as email grouping (to consolidate messages), detailed tracking of email delivery status (bounces, spam complaints, opens, etc.), and more.
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Managing Shared Mailboxes and Service Accounts
- Recognize that emails sent from shared mailboxes, email-enabled groups, and room mailboxes contribute to the ERRLs.
- Assess the volume of external emails sent from such non-licensed mailboxes.
- If high-volume sending to external recipients is necessary from a service account, consider utilizing a licensed mailbox with optimized sending patterns or exploring the use of add-ons.
Monitoring and Troubleshooting
- Regularly monitor the “Tenant Outbound External Recipients” report in the EAC to stay informed about the tenant’s TERRL usage.
- Utilize the `Get-LimitsEnforcementStatus` PowerShell cmdlet for automated monitoring of the TERRL status.
- Understand the NDR error code 550 5.7.233, which indicates that the tenant has exceeded its daily external recipient rate limit. Establish internal processes for addressing and potentially resending failed communications.
Conclusion: Planning for Sustainable Automated Email Communication
For Oracle EBS and Oracle Fusion Cloud users, a thorough understanding and proactive management of the new Microsoft 365 email limits are crucial for ensuring the smooth operation of automated business processes. By assessing current email-sending patterns, implementing optimization strategies, and considering alternatives like AventX, organizations can mitigate the risks associated with these limits and maintain effective external communication. It is essential to remain aware of the evolving nature of cloud service limitations and to continuously monitor and adapt email-sending practices accordingly.
Furthermore, exploring solutions like AventX can provide valuable additional functionality, such as insights into email delivery with detailed tracking of bounces, spam reports, and recipient engagement.
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