Microsoft 365 Error Codes

How to Fix Microsoft 365 NDR Error 550 5.7.708 (Service Unavailable)

Maira Mehtab Sep 27, 2026 870 views

Question details

The user needs to resolve a non-delivery report (NDR) error 550 5.7.708 in Microsoft 365, which blocks outbound emails due to IP or traffic policies.

Product: Microsoft 365
Device & OS: not provided
Scenario: Attempting to send an outbound email from a Microsoft 365 account and receiving a bounce-back message instead.
Observed behavior: The email fails to deliver and returns a '550 5.7.708 Service Unavailable' error, indicating the sending IP address or message traffic was blocked by reputation controls.

Before you start

Before proceeding, ensure you have saved a complete copy of the Non-Delivery Report (NDR) message and identified your public IP address, as support teams will require these details.

Solution 1Recommended

Contact Your Microsoft 365 Administrator to Open a Service Request

Since this error involves tenant-level IP blocking or reputation control, your Microsoft 365 administrator must request an unblock directly from Microsoft Support.

Error 550 5.7.708 typically occurs when a tenant's sending IP or domain is temporarily restricted by Microsoft due to a suspected spam outbreak, a newly created trial tenant, or negative sender reputation. Standard users cannot bypass this block independently.

Log into the Admin Center

Navigate to Help & Support

Click on the 'Support' section in the left navigation menu and select 'Help & support'.

Create a New Service Request

Open a new ticket explaining that your tenant is restricted and you are receiving NDR error 550 5.7.708.

Provide Necessary Diagnostic Details

Submit the complete text of the NDR, your sending domain, public IP address, recipient domain, exact message time, and any available message-trace details to expedite the unblocking process.

Reseller Subscriptions: If your Microsoft 365 subscription was purchased through a third-party reseller, you will likely need to contact that reseller directly to open the support request on your behalf.

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Frequently Asked Questions

What does Microsoft 365 error 550 5.7.708 mean?

This error signifies that your outbound email could not be delivered because your sending IP address or overall message traffic was blocked by Microsoft's automated reputation controls or service security policies.

Can a standard user fix error 550 5.7.708 on their own?

No, this error requires tenant-level administrative intervention. You must contact your organization's Microsoft 365 global admin to investigate the issue and submit an unblock request to Microsoft Support.

Why did my Microsoft 365 tenant get blocked from sending emails?

Common triggers include sending a high volume of bulk emails from a new or trial tenant, suspected account compromises leading to spam outbreaks, or routing mail through an IP address with a historically poor sender reputation.

What specific information is needed for the Microsoft Support ticket?

To quickly resolve the block, you should provide the full Non-Delivery Report (NDR) text, your sending domain, the public IP address from which the email originated, the recipient's domain, the exact timestamp of the failure, and a message trace report.

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