Microsoft 365 Error Codes

Fix Exchange Online Error 550 5.7.705 Tenant Threshold Access Denied

Phi Hung Vo Sep 28, 2026 869 views

Question details

The user is encountering an Access denied Non-Delivery Report (NDR) due to a tenant-level block on sending emails.

How to Resolve Exchange Online Error 550 5.7.705 Tenant Threshold

Product: Microsoft 365 Exchange Online
Device & OS: not provided
Scenario: A mail relay sends a sudden, high volume of messages through Exchange Online Protection, triggering Microsoft's spam prevention thresholds.
Observed behavior: Outbound emails are blocked, returning a 550 5.7.705 Access denied (tenant threshold exceeded) error code.

Before you start

Ensure you have Global Administrator privileges in your Microsoft 365 tenant, as resolving this tenant-level threshold error requires administrative access to investigate logs and contact support.

Solution 1Recommended

Investigate and Remediate the High Email Volume

Identify the root cause of the sudden spike in outgoing email traffic and apply Microsoft's official remediation steps for threshold errors.

Before the block can be lifted, it is crucial to determine why your tenant exceeded the sending threshold. This is often caused by compromised accounts or improperly configured bulk mailing applications.

Identify the traffic source

Check your mail relay systems and Exchange message trace logs to identify which accounts or connectors are sending the sudden high volume of messages.

Secure compromised accounts

If you detect unauthorized access, immediately reset the affected users' passwords, revoke their active sessions, and enforce Multi-Factor Authentication (MFA).

Review Microsoft NDR documentation

Consult Microsoft's official guidance for NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750 for specific remediation actions relevant to your tenant's configuration.

Investigate and Remediate the High Email Volume

Bulk Email Best Practices: Exchange Online is not designed for sending bulk marketing emails. If you need to send newsletters or mass communications, consider using a dedicated third-party bulk email provider.

Solution 2

Open a Microsoft 365 Service Request

If internal remediation steps do not lift the restriction, escalate the issue to the Microsoft 365 backend team or your subscription reseller.

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Frequently Asked Questions

What triggers the 550 5.7.705 error in Exchange Online?

This error occurs when an organization's Microsoft 365 tenant exceeds the acceptable threshold for sending emails. It is a protective measure by Exchange Online Protection (EOP) to stop potential spam or malicious campaigns, usually triggered by a mail relay sending a sudden, high volume of messages.

Can a standard user fix the Tenant Threshold error?

No, standard end-users cannot resolve this issue. A Microsoft 365 Global Administrator must investigate the root cause, secure any breached accounts, and contact Microsoft Support to remove the tenant-level email block.

How long does it take for Microsoft to unblock a restricted tenant?

Once you have addressed the underlying issue (e.g., stopping a spam script or securing an account) and submitted a formal service request, the Microsoft backend team typically reviews the case and lifts the restriction within 24 to 48 hours.

How can I prevent the 550 5.7.705 threshold error in the future?

To prevent this error, ensure your mailing practices comply with Microsoft's Exchange Online sending limits. Use dedicated third-party bulk email services for marketing campaigns instead of routing them through standard Microsoft 365 mailboxes, and strictly monitor user accounts for unauthorized access.

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