How to stop emails to hotmail.com bouncing back

Question

I'm suddenly receiving the below error message when sending emails to hotmail.com email addresses.

550 Unfortunately, messages from [103.250.212.12] 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=11BC459D8F80CACB] [AMS0EPF00000194.eurprd05.prod.outlook.com 2025-11-13T23:44:20.066Z 08DE22CEC82AD568]

I've tried to diagnose the problem but haven't had any success so am hoping somebody may have had the same experience and is able to assist. The problem only started a few days ago and is only happening with hotmail.com email addresses. Interestingly, the problem only occurs when I'm working from home. If I send the same email when at work (which uses a different ISP), I'm not having any problems. I contacted my home ISP but they were unable to assist.

And I haven't been able to work out how I can send an email or online chat with somebody from Microsoft to get support.

Any suggestions would be greatly appreciated.

Answer 1

To stop emails from bouncing back to hotmail.com addresses, you need to address the issue of your IP address being on a block list. The error message you received indicates that your ISP's network is part of a block list, which is preventing your emails from being delivered to hotmail.com addresses. Here are some steps you can take:

1. Contact Your ISP: Since the error message suggests contacting your Internet Service Provider (ISP), it's important to follow up with them. They may need to investigate why your IP address is listed and take steps to remove it from the block list.
2. Use the Delist Portal: If your ISP is unable to resolve the issue, you can request removal from the block list yourself. Microsoft provides a delist portal where you can submit a request to have your IP address reviewed and potentially removed from the block list. More information can be found in the Microsoft documentation.
3. Check Reverse DNS: Ensure that your ISP is not advertising your IP address as a non-routable IP. This can sometimes happen if the reverse DNS lookup fails, which can lead to delivery issues.
4. Monitor Email Practices: Make sure that your email practices comply with best practices to avoid being flagged as spam. This includes avoiding sending bulk emails and ensuring that your email content is not triggering spam filters.
5. Test from Different Networks: As you mentioned, sending emails from your work network does not result in bounce backs. This indicates that the issue is specific to your home ISP. Testing from different networks can help confirm this.
6. Seek Microsoft Support: If the issue persists, consider reaching out to Microsoft support for further assistance. They may be able to provide insights or help troubleshoot the issue further.

By following these steps, you should be able to resolve the issue and prevent your emails from bouncing back to hotmail.com addresses.

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References:

• External senders - Troubleshoot email sent to Microsoft 365
• Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors

Answer 2

Hi Kerry,

You are running into a Microsoft Outlook reputation block on your home network. The error shows Outlook saw the connection coming from your home public IP 103.250.212.12 and rejected it with S3150, which is a block applied to the sending IP. That is why it works from work but not from home.

The simplest way to fix this on your side is to stop sending mail directly from your home IP and instead submit mail through your email provider's authenticated SMTP server , so Outlook sees your provider's trusted mail servers rather than your ISP address. Microsoft's guidance calls this client SMTP submission and it is the supported way for POP or IMAP accounts to send mail from any network.

Open Outlook > File > Account Settings > Account Settings again, highlight your mail account, choose Change, then More Settings. On the Outgoing Server tab tick My outgoing server requires authentication and use the same username and password as your incoming mail. On the Advanced tab set the outgoing server to port 587 and encryption to TLS or STARTTLS.

Make sure the Outgoing server name is your provider's submission host, for example smtp.office365.com if you use Microsoft 365, or the SMTP host your mail company documents. Save and test. From now on your messages will relay through the provider's mail system and should deliver to hotmail.com even when you are at home.

If you happen to be using a webmail interface like Outlook on the web, that already uses authenticated submission and should work from home immediately.

If you still see rejections after making the change, the rejection would be tied to the IP in the bounce. In that case only the IP owner can request removal using Microsoft's delist portal, but try the authenticated submission fix first because it avoids the block entirely for you.

If you tell me which mail provider you send through, I can give you the exact server name and a quick check that your Outlook profile is using POP or IMAP and not Exchange.