We are getting a message: Please contact your Internet service provider since part of their network is on our block list (S3150)

If you are receiving a message indicating that your server's IP address (87.253.157.239) is on a block list, this typically means that Microsoft has identified your IP as a potential source of spam or malicious activity. To resolve this issue, you can take the following steps:

1. Check the Non-Delivery Report (NDR): Review the NDR message you received for specific error codes and instructions.
2. Use the Anti-Spam IP Delist Portal: You can request removal from the Microsoft 365 blocked senders list by visiting the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com. Follow the instructions provided there to submit your request.
3. Contact Your ISP: Since the message suggests contacting your Internet Service Provider (ISP), they may need to investigate why their network is being flagged and potentially assist in resolving the issue.
4. Follow Best Practices: Ensure that your email practices comply with Microsoft’s guidelines to avoid being flagged in the future. This includes proper email authentication and maintaining a good sender reputation.

By following these steps, you should be able to address the blocking issue and improve your email deliverability to Microsoft accounts.

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data. 

Hi Bas Broekarts

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

From my research, I found several factors that could influence this issue. You can review the article and verify whether your email aligns with Microsoft’s policies and guidelines: Troubleshooting

If your email complies with the policies and guidelines but you still encounter delivery issues not addressed in the FAQ provided in the article, please contact support here to request an unblock: New support request

I hope this information proves helpful. If you need further assistance, feel free to ask in the comments section.

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