How to I contact Microsoft about Block List S3150

Question

How to I contact Microsoft about Block List S3150

Penny Healy, VodafoneThree 20

Hello

How do I speak to someone about a Hard Bounce error.

The web address on the error message is down and the form I submitted at https://olcsupport.office.com/ on Thursday has not had an acknowledgement or response.

550 5.7.1 Unfortunately, messages from [] 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.

Thank you

Moved from: Microsoft 365 and Office | Microsoft Forms | For business

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Answer accepted by question author

Anonymous

Hi Penny Healy, VodafoneThree

Thank you for reaching out to Microsoft Q&A Forum. Based on the bounce you shared (550 5.7.1 … network is on our block list (S3150)), this means the public outbound sending IP used by your mail service is currently on Microsoft’s block list, so Outlook.com/Hotmail will reject mail at the SMTP stage.

Here's what you should do:

Use the Office 365 Anti‑Spam IP Delist Portal

Go to: https://sender.office.com
Follow the instructions on the page. Enter:
- the blocked IP shown in the bounce
- the email address that received the NDR/bounce
Submit the request for review.

If you don’t control the sending IP, your ISP/email provider must do it. Your bounce explicitly says to contact your Internet service provider because the block is tied to their network/IP space. If VodafoneThree (or your mail host) is the actual outbound sender, they need to submit the delist request and also investigate why that IP/range was flagged.

Please kindly note that this is a public 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.

Please feel free to let me know how it goes. Thank you so much for your time and understanding!

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Penny Healy, VodafoneThree 20 Reputation points

2026-02-18T09:26:52.5566667+00:00

Thank you Winnie-B

I have emailed my IT dept with you response.

Would you be able to offer any additional help on whether the ISP in this case is my companies IT dept. or Marketo the MA platform we use to send our emails via a dedicated IP? I am being given conflicting information.
Anonymous

2026-02-19T07:40:51.2433333+00:00
Hi Penny Healy, VodafoneThree

Thank you for your comment. At this point, please contact support team directly for further assistance via Contact - Microsoft Support

Type a brief description in the search box.

Click "Get Help", then scroll to the bottom and select "Contact Support”.

Choose the appropriate categories/products.

It may offer live chat and, depending on your subscription/region, an option to request a callback: Look for and select "Chat with a support agent in your web browser" (during business hours) or a similar callback option (if available).

Thank you so much for your time and understanding!

1 additional answer

Your answer

Penny Healy, VodafoneThree 20 Reputation points

2026-02-18T09:26:52.5566667+00:00

Thank you Winnie-B

I have emailed my IT dept with you response.

Would you be able to offer any additional help on whether the ISP in this case is my companies IT dept. or Marketo the MA platform we use to send our emails via a dedicated IP? I am being given conflicting information.
Anonymous

2026-02-19T07:40:51.2433333+00:00

Hi Penny Healy, VodafoneThree

Thank you for your comment. At this point, please contact support team directly for further assistance via Contact - Microsoft Support

Type a brief description in the search box.

Click "Get Help", then scroll to the bottom and select "Contact Support”.

Choose the appropriate categories/products.

It may offer live chat and, depending on your subscription/region, an option to request a callback: Look for and select "Chat with a support agent in your web browser" (during business hours) or a similar callback option (if available).

Thank you so much for your time and understanding!

Answer 1

To address the Hard Bounce error related to the block list S3150, you can follow these steps:

Contact Your Internet Service Provider (ISP): Since the error message suggests that part of their network is on the block list, it's important to reach out to your ISP for assistance. They may need to take action to resolve the issue.
Use the Delist Portal: If you are an external sender and your IP address is blocked, you can request removal from the Microsoft 365 blocked senders list using the Office 365 Anti-Spam IP Delist Portal. This portal allows you to submit a request for delisting.
Check for Non-Delivery Reports (NDR): If you receive a non-delivery report (NDR), follow any instructions provided in the report. This may include contacting Microsoft support directly for further assistance.
Microsoft Support: If you continue to have issues, you can ask the Microsoft 365 recipient to contact Microsoft Support on your behalf, as external senders typically cannot open support tickets directly.

For further troubleshooting, you can refer to the External senders - Troubleshoot email sent to Microsoft 365 documentation.

References: