Immediate answer
TERRL is a tenant boundary, not a mailbox setting.
Exchange Online's Tenant External Recipient Rate Limit—TERRL—counts external recipients across the tenant in a rolling 24-hour window. Microsoft calculates the available quota from the tenant's eligible email licenses and exposes the current value and usage through Exchange reporting.
Application mail, scheduled reports, printers, scanners, connector relay, and ordinary user mail can all contribute when Exchange Online delivers to recipients outside the tenant. Moving the same traffic between mailboxes does not turn a tenant-wide limit into separate capacity.
Microsoft updated the TERRL calculation and rollout information in August 2026, with the revised rollout beginning in September 2026. Treat older fixed-limit articles as historical and verify the value shown for your tenant.
Limit layers
Identify the counter that actually stopped the message.
| Boundary | Scope | Typical evidence |
|---|---|---|
| TERRL | External recipients across the tenant over a rolling 24 hours | 550 5.7.233 and the Tenant Outbound External Recipients report |
| Mailbox recipient rate | Recipients submitted by one mailbox over a rolling day | Per-sender throttling or outbound restriction evidence |
| SMTP message rate | Client-submission messages from one mailbox | Submission throttling around the documented messages-per-minute boundary |
| Outbound spam policy | Configured internal, external, and daily recipient thresholds | Policy action and restricted-entity evidence |
onmicrosoft.com domain limit | External recipients sent from the tenant's default MOERA domains | 550 5.7.236 |
One delivery can encounter more than one layer. Diagnose the complete SMTP response and the reporting data rather than assuming every capacity error is the familiar 30-messages-per-minute SMTP AUTH limit.
Error identity
Do not treat 5.7.233 and 5.7.236 as the same problem.
550 5.7.233
The tenant exceeded its external-recipient quota. The count uses a rolling 24-hour window, so service resumes as older recipients fall outside that window.
550 5.7.236
The tenant exceeded the separate limit for external mail sent from its default onmicrosoft.com domains. Microsoft documents a tenant-wide maximum of 100 external recipients in a rolling 24-hour window for that boundary.
Distribution-list expansion matters: a group can represent many external recipients after expansion. Preserve the original NDR, timestamp, envelope sender, recipient set, submission method, and message trace evidence before changing configuration.
Tenant evidence
Measure the shared demand before choosing a remedy.
Use the Exchange admin center's Tenant Outbound External Recipients report to see the tenant limit and usage. Use message trace and sender reports to identify the workflows contributing to the count. Review enough history to include monthly reporting, monitoring storms, payroll runs, and other uneven workloads.
- 01
Separate internal and external demand
HVE can address high-volume internal mail, but it does not provide external delivery.
- 02
Find expansions and fan-out
Count delivered recipients, not merely the number of submitted messages or visible distribution-list addresses.
- 03
Attribute automated senders
Map each mailbox or relay identity to applications, devices, owners, peaks, and business purpose.
- 04
Classify the workload
Separate ordinary operational notifications from bulk, marketing, or externally scaled transactional email that needs a different service.
Delivery engineering
Back pressure should be visible and bounded.
A durable sender can retain eligible work during a temporary capacity condition and retry with bounded delay. It should not hammer Exchange, create parallel identities to evade limits, or hide a permanent design mismatch. Operators need queue age, failure classification, affected recipients, and a safe way to stop or reroute inappropriate traffic.
For high-volume internal mail, evaluate Microsoft 365 High Volume Email. For high-volume external application email, Microsoft points customers toward Azure Communication Services Email or an appropriate specialist service. The correct choice depends on identity, recipient scope, volume, data path, and operational ownership.
Product boundary
RelayBridge improves resilience, not quota.
RelayBridge can durably queue messages accepted from explicitly configured local clients and retry temporary Microsoft-facing failures. It does not raise TERRL, divide one tenant into independent quotas, or turn Exchange Online into a bulk-mail platform.
RelayBridge is most relevant to modest operational mail from legacy devices and applications that need a local SMTP compatibility boundary. Review the SMTP AUTH limits guide for mailbox-level constraints and the mail-flow comparison before selecting a path.
Response plan
Handle a tenant-limit event without creating another one.
- 01
Preserve the complete rejection
Keep the enhanced code, full text, sender, recipients, timestamp, and trace identifiers.
- 02
Confirm the affected counter
Compare TERRL, mailbox limits, outbound-spam policy, and the separate MOERA-domain boundary.
- 03
Pause uncontrolled retries
Use bounded backoff and prevent duplicate fan-out while the rolling window recovers.
- 04
Remove the structural cause
Reclassify internal high-volume mail, external application mail, and ordinary operational SMTP into suitable services.
Clarifications
Frequently asked questions.
Can another mailbox avoid TERRL?
No. TERRL is tenant-wide. A different mailbox may have its own unused mailbox quota, but the same external recipients still contribute to the tenant counter.
Does one distribution group count as one external recipient?
Not necessarily. Microsoft documents that external recipients are counted after group expansion for TERRL.
Will a local queue guarantee later delivery?
No. It can preserve work and retry eligible temporary failures. The message can still encounter authorization, recipient, spam, policy, or downstream-delivery failures.
Authoritative sources