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Fix Microsoft 365 Error 451 4.4.4 No Mail-Enabled Subscriptions
Question details
Emails sent to a Microsoft 365 domain are being rejected with error 451 4.4.4, stating there are no eligible mail-enabled subscriptions.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Routing outgoing messages through third-party services like SendGrid to a Microsoft 365 recipient domain.
- Observed behavior
- The Microsoft 365 server rejects the messages, displaying error code 451 4.4.4 due to missing or unrecognized mail-enabled subscriptions for the tenant.
Verify that your Microsoft 365 subscription is currently active and includes Exchange Online services before escalating the issue. Collect the specific error message, message trace details, and sender IP addresses to provide to the support team.
Escalate to Microsoft Support via Global Administrator
Because this error requires backend tenant investigation and license verification, an Office 365 Global Administrator must open a service request with Microsoft Support.
This issue typically arises when the recipient domain's tenant lacks the necessary mail-enabled subscription licenses, or when there is a backend synchronization delay in Microsoft's systems.
Since end-users do not have the administrative permissions required to inspect tenant configurations or server-side logs, the issue must be handled by an IT administrator.
Log in to the Microsoft 365 admin center using a Global Administrator account.
Navigate to the 'Support' tab on the left-hand menu and click on 'Help & support' or 'New service request'.
Submit the support ticket, including relevant message traces, server logs, and documentation showing that emails are bouncing with the 451 4.4.4 error when sent via your mail service (e.g., SendGrid).
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Frequently Asked Questions
What does Microsoft 365 Error 451 4.4.4 mean?
This error code indicates that the destination email server is temporarily unable to route the message because the recipient's Microsoft 365 tenant does not have an active, recognized mail-enabled subscription (such as Exchange Online).
Why does this error happen when sending through services like SendGrid?
When third-party mailing services like SendGrid route emails to a Microsoft 365 domain, Microsoft's Exchange servers verify the recipient tenant's subscription status. If the tenant lacks proper licensing or has backend configuration errors, Microsoft's servers will reject the incoming message.
Can a standard end-user fix error 451 4.4.4?
No, this is a tenant-level configuration or licensing issue. End-users cannot resolve it directly and must contact their organization's IT department or Microsoft 365 Global Administrator to address the licensing issue with Microsoft Support.
