Published rule snapshot
- External recipients are addresses whose domains are not accepted domains in the tenant.
- Trial tenants have a published 5,000-external-recipient daily limit.
- For non-trial tenants, Microsoft publishes the formula 500 × (non-trial email licenses^0.7) + 9,500.
- If a tenant exceeds the current limit, later external messages can be blocked with 550 5.7.233 until rolling usage falls below the limit.
A report is the start, not the remediation plan
The EAC report and Microsoft support script can expose enforcement values, estimated usage, and contributing senders or domains. They do not know the business owner, whether a source should stay or move, who will execute the change, or what evidence proves a cutover worked.
- Confirm the live enforcement value and threshold.
- Export or estimate the contributing sender data.
- Identify the business and technical owner for each material source.
- Evaluate the route using current provider requirements.
- Define a test, rollback condition, and post-change verification.
Common questions
Does each unique recipient count only once?
No. Microsoft describes message-recipient pairs during the rolling window, not a lifetime list of unique addresses.
Is an estimate the live counter?
No. The support script describes its result as an estimate. Use live enforcement status for the current value, threshold, verdict, and state.
Will moving a sender guarantee delivery?
No. Eligibility, authentication, provider limits, content, reputation, and implementation all matter. This guide does not guarantee delivery or migration success.
Sources
- Microsoft Exchange Team: Introducing Exchange Online tenant outbound email limits — checked 2026-09-07.
- Microsoft CSS-Exchange: Get-TerrlExternalRecipientEstimate — checked 2026-09-07.