Outbound emails are restricted

Question

Diagnostic information for administrators:

Generating server: CW1P302MB2198.GBRP302.PROD.OUTLOOK.COM

******@hotmail.co.uk Remote server returned '550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP. For more information please go to http://go.microsoft.com/fwlink/?LinkId=526653AS(8562)[CWLP302MB0182.GBRP302.PROD.OUTLOOK.COM2026-02-26T14:35:53.098Z 08DE74C7E7B0595D]'

Original message headers:

Received: from 

Answer 1

The non-delivery report shows error 550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP, which means outbound mail from the sending IP address has been blocked by Microsoft due to suspicious or unwanted traffic.

Because the sender is external to Microsoft 365 (a Hotmail/Outlook.com address sending to Microsoft 365), the correct remediation is:

1. Collect the full NDR, including:
   • The exact error text (550 5.7.708 ... traffic not accepted from this IP)
   • The source IP address shown in the NDR or message headers.
2. As the sending admin (or the provider managing that IP), request delisting using the Microsoft delist process:
   • If the NDR instructs to email delist@microsoft.com, forward the full NDR to delist@microsoft.com and include the source IP.
   • If the NDR instructs to use the Office 365 Anti-Spam IP Delist Portal (https://sender.office.com), follow that instruction and submit the IP for review.
3. Ensure the sending environment is clean before or in parallel with delisting:
   • Check that no accounts or systems are compromised and sending spam.
   • Verify proper email authentication (SPF/DKIM/DMARC) and that the IP is not advertising a non-routable/private address.
4. Wait for Microsoft’s review. For delist requests sent to delist@microsoft.com, Microsoft typically responds with next steps within about 48 hours. For portal submissions, the block is removed if the traffic is deemed legitimate.

If the sender is using Outlook.com/Hotmail as a consumer service and believes the block is in error, the Outlook.com delisting/support form can also be used as documented in the context.

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References:

• External senders - Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors
• External senders - Use the delist portal to remove yourself from the blocked senders list
• Fix NDR error "550 5.7.1" in Exchange Online
• External senders - Troubleshoot email sent to Microsoft 365
• Sender Support in Outlook.com