Microsoft 365 - External Recipient Rate Limit FAQs

Table of Contents

General Overview

1. What is Microsoft’s External Recipient Rate (ERR) limit?
   1. The ERR limit is a policy that limits the maximum number of external recipients a user can email from an Exchange Online mailbox within a rolling 24-hour period. Currently, WSU’s limit is 5,000 external recipients. 
2. What qualifies as an Exchange Online mailbox at WSU?
   1. A WSU Exchange Online mailbox refers to a Microsoft 365 email account created for a WSU Network ID, Shared Mailbox, Room Mailbox, or Equipment Mailbox.
3. Who is considered an internal vs. external recipient at WSU?
   1. External recipients are considered email addresses that deliver to an external destination that is not a WSU Exchange Online mailbox. Internal recipients are considered email addresses that deliver to a WSU Exchange Online mailbox.
4. Does the ERR limit apply to emails sent to internal recipients?
   1. Emails sent to internal recipients via a WSU Exchange Online mailbox do not count toward the ERR limit.
5. Which types of emails count toward the ERR limit?
   1. Any email sent to an external recipient counts toward the limit, including direct messages, CCs, BCCs, and emails sent to Office 365 distribution groups that expand to external recipients.

Impact

1. Who at WSU is affected by the ERR limit?
   1. Users, departments, or organizations at WSU who regularly send emails to a large external recipient audience via a WSU Exchange Online mailbox may be impacted.
2. Can I request an exception or increase to the ERR limit?
   1. No, the external limit is a service limit and cannot be increased.
3. Will Microsoft notify me if I am approaching the ERR limit?
   1. Microsoft does not currently send warnings before the limit is reached. Users are encouraged to monitor their sending proactively.
4. What happens if I exceed the ERR limit?
   1. If you exceed the ERR limit, email delivery to external recipients will be restricted for up to 24 hours. Email delivery to internal recipients will remain unaffected.
5. Does the ERR limit reset daily, and at what time?
   1. The ERR limit is a rolling limit resets based on the prior 24 hours, based on the time of your first email to external recipients sent within that period.
6. Who can I contact at WSU for help evaluating the impact of this change for my team?
   1. For any questions, concerns, or assistance regarding the ERR limit, please submit a request to Crimson Service Desk.

Technical Considerations

1. Does the ERR limit apply to mailing lists or distribution groups?
   1. The ERR limit may apply depending on the configuration of the mailing list or distribution group. For Office 365 distribution groups with external recipients, each unique external address counts toward your ERR limit. If communicating to a WSU Mailman listserv with external recipients, this will count as a single internal recipient. If communicating to mailing lists set up via a third-party email service, this will not count towards your ERR limit.
2. Are automated systems or applications affected by the ERR limit?
   1. Any system or application that sends email to external recipients via a WSU Exchange Online mailbox is subject to the ERR limit.
3. Will this impact DMARC or DKIM when using external services that send on behalf of a WSU email address?
   1. The ERR limit does not impact DMARC or DKIM configurations.
4. What tools or strategies can I use to stay within the ERR limit?
   1. Please consider segmenting your mailing lists, using third-party email services, or scheduling messages across multiple days.

Exploring Alternatives and Support

1. What alternatives are available if I need to email a large number of external recipients?
   1. WSU recommends transitioning to third-party email service if the ERR limit impacts you. These services operate independently of Exchange Online, have their own sending limits and policies, and are built to handle high-volume email campaigns.
2. What third-party email services are currently used at WSU?
   1. Based on a recent survey, teams across WSU use services like Mailchimp, Constant Contact, Brevo, HubSpot, and Campaign Monitor for external communications.
3. Is there a list of WSU-approved third-party email services?
   1. WSU does not currently maintain a general list of pre-approved third-party email services. Each service is evaluated individually by Information Security Services (ISS) based on the specific use case, the nature of the data involved, and the level of risk associated with its use.
4. What should I keep in mind when selecting an external email service?
   1. Please consider compliance with WSU data privacy and security policies, accessibility, and integration with WSU systems. ISS is available to assist in reviewing and assessing potential services to ensure they meet university security requirements.
5. Who should I contact help completing a security review on a third-party email service?
   1. For assistance reviewing a third-party email service for data privacy and security compliance, please submit a request to Crimson Service Desk. Requests will be escalated to ISS as appropriate.
6. What is Azure Communication Services (ACS), and is WSU considering it as an option?
   1. ACS is a Microsoft platform for building communication solutions. Microsoft has positioned ACS as a potential alternative for navigating the reduced ERR limit. At this time, WSU is not offering access to ACS nor licensing for its use. Learn more about ACS.
7. Is WSU planning to adopt a university-wide solution for external email communications?
   1. Following discussions with leadership, WSU has determined that a centralized enterprise solution for external email communications will not be pursued at this time. While financial considerations and the complexity of implementing a single systemwide solution were factors for this decision, this approach allows individual teams the flexibility to choose communication tools that best meet their diverse needs.