IP Blocked S3150

HostCoral Web Services 0 Reputation points
2026-09-13T19:15:37.46+00:00

Hello,

I have been receiving multiple customers with the following error.

hotmail-com.olc.protection.outlook.com[REMOVED PII] said: 550 5.7.1    Unfortunately, messages from [Ip.address] 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=REMOVED PII]    [REMOVED PII] (in reply to MAIL FROM command) After submitting a de-block request it says that my IP address in not blocked but the subnet of the server.

Please let me know if there is anything you can do to solve this issue

Outlook | Web | Outlook.com | Email
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  1. Ian-T 11,560 Reputation points Microsoft External Staff Moderator
    2026-09-14T00:45:54.8333333+00:00

    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. Please note that this is a user-to-user support forum. Moderators and contributors cannot access accounts or Microsoft’s back-end systems. We can only provide technical guidance on reported incidents, requests and ideas 

    Hi @HostCoral Web Services

    The S3150 rejection indicates that Microsoft is blocking the sending network used by your mail server. Since the delisting check reports that the individual IP is clear but the subnet is affected, this needs to be handled by the owner of that IP range, usually your hosting provider or upstream ISP.

    Please submit a deliverability request through Outlook.com Sender Support and include:

    • The complete NDR shown above
    • The affected sending IP and domain
    • Recent sample timestamps
    • Confirmation that the portal reports the IP as not blocked while the S3150 rejection continues

    After submission, follow the instructions in the automated response exactly. If asked to reply, do so without changing the subject or message body, as that moves the request to further review.

    I hope you find this information useful. If you have any more questions, don't hesitate to reach out.

    Wishing you a lovely day!

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