How can i remove from S3150 block list

Question

Hi,

I have my mail server blocked to send emails to hotmail and received the above message.

How can i delist if the link isnt working?

"

This is the mail system at host mail.pcsolution.pt.

I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own text from the attached returned message.

               The mail system
[<<Mod remove PII> @hotmail.com>]: host
    hotmail-com.olc.protection.outlook.com[52.101.194.5] said: 550 5.7.1
    Unfortunately, messages from [94.23.76.202] weren't sent. Please contact
    your Internet service provider since part of their network is on our block
    list (S3150). You can also refer your provider to
    [http://mail.live.com/mail/troubleshooting.aspx#errors]. [Name=Protocol
    Filter Agent][AGT=PFA][MxId=<Mod remove PII>]
    [CH3PEPF00000009.namprd04.prod.outlook.com 2026-02-16T14:21:15.765Z
    08DE6C2B37ABF5F0] (in reply to MAIL FROM command)


yaml
Reporting-MTA: dns; mail.pcsolution.pt
X-Postfix-Queue-ID: 615064C7048
X-Postfix-Sender: rfc822; 

Return-Path: 

Answer 1

Dear Ricardo Lima,

Welcome to Microsoft Q&A Support. 

Thank you for sharing the details with me. Since I noticed that you are communicating in English, I will also respond in English to ensure our conversation remains clear and consistent.

Based on the information you provided, it appears you are experiencing an issue when sending emails to a personal domain, and you are receiving the following error: "550 5.7.1 – Unfortunately, messages from your server were not sent. Please contact your Internet service provider since part of their network is on our block list (S3150)"

Please note that this is a user‑to‑user support forum. Moderators, community contributors, and external Microsoft employees cannot access back‑end systems or directly modify Microsoft product features. Our role is to provide technical guidance based on the information shared.

The S3150 error indicates that the IP address of your mail server has been blocked by Outlook.com/Hotmail’s automated spam‑filtering systems. To resolve this issue, your IT administrator must request IP delisting by following the steps below:

1. Go to the Office 365 Anti‑Spam IP Delist Portal: https://sender.office.com/
2. Carefully follow the instructions on the page.
   1. Enter the blocked IP address.
   2. Enter the email address that received the Non‑Delivery Report (NDR).
3. Submit the request for review.

It is also important that your organization investigates the underlying cause of the block, such as potential spam activity or compromised accounts, to prevent future occurrences. I hope this information helps. If you have any additional questions, please feel free to reach out. Please feel free to reach out.

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Answer 2

To remove your mail server from the S3150 block list, you should follow these steps:

1. Contact Your Internet Service Provider (ISP): Since the block is related to your ISP's network, you should reach out to them for assistance. They may need to investigate why your IP address is on the block list and take appropriate actions to resolve the issue.
2. Use the Delist Portal: If you are receiving a different error code related to being on a blocked senders list, you can use the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com to request removal from the blocked senders list. However, for S3150 specifically, you may need to follow your ISP's guidance.
3. Follow Additional Instructions: If the delist portal link is not working, ensure that you are using the correct link and that there are no network issues on your end. If problems persist, consider contacting Microsoft support for further assistance.
4. Monitor Your Email Practices: Ensure that your email practices comply with best practices to avoid future blocks. This includes proper email authentication and avoiding spam-like behavior.

If you continue to have issues, it may take some time for the block to be lifted, and you should keep in touch with your ISP for updates on the situation.