550 5.7.708 – Access denied, traffic not accepted from this IP

Hi @Kirsten Nelis,

Thank you for posting your question in the Microsoft Q&A forum.

To clarify the situation, the NDR 550 5.7.708 “Access denied, traffic not accepted from this IP” error occurs when Exchange Online blocks outbound email because the sending IP address has a low reputation. Microsoft notes that this behavior is more common for new, trial, or recently created tenants, where outbound sending can be temporarily restricted while the tenant’s reputation is being established. You can find more information in Microsoft’s documentation here: NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750.

Because this is an Exchange Online outbound protection block, it cannot be resolved from the Outlook client itself. Instead, the corrective action must be taken by a tenant email administrator.

To move forward, please start by confirming that the affected mailbox has an Exchange Online license assigned and fully provisioned, especially if this tenant is new or currently in a trial phase.

Next, an administrator will need to open a support ticket directly with Microsoft and request an IP address exception or unblock for error 5.7.708. Microsoft has indicated that Support can apply a temporary exception while licensing and reputation are being established. When submitting the ticket, it’s important to include:

• The full NDR message
• The affected sending mailbox
• Whether the email is being sent via Outlook, Outlook on the web, or through a connector or third‑party integration

You can create a support ticket by signing in to the Microsoft 365 admin center and following the steps in this link: Get support for Microsoft 365 for business to create a support ticket from the admin center or by calling phone support to contact Microsoft Support: Customer service phone numbers. If you don't have admin privileges, you can ask your IT admin to do it on your behalf.

Alternatively, you can learn how to find your administrator through this link: How do I find my Microsoft 365 admin?.

Note: We appreciate your understanding regarding the scope of support available through this forum. As moderators, our role is to provide general guidance and assist with common troubleshooting steps. While we do not have access to internal systems or administrative tools necessary to resolve specific account or backend-related issues, we will continue to do our best to support you within the scope of our responsibilities.

I hope this information helps move things forward. Please feel free to let me know how it goes, or if you need any further assistance. I’ll be happy to help.

I look forward to your reply.

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how can i unblock 550 5.7.708 – Access denied, traffic not accepted from this IP