Fix Outlook and Hotmail Bounce Error S3150 (IP Block List)
Question details
The user needs to resolve an issue where emails sent from a new server IP are rejected by Outlook and Hotmail with a bounce error S3150.
- Product
- Outlook and Hotmail
- Device & OS
- not provided
- Scenario
- Sending emails to Microsoft domains from a new server IP after updating DNS records.
- Observed behavior
- Emails are consistently rejected with bounce error S3150, indicating the sending IP is blocked by Microsoft's network.
Before requesting an IP delisting, ensure that your mail server is not compromised and that your domain's SPF, DKIM, and reverse-DNS (PTR) records are fully propagated.
Verify Email Records and Request Microsoft Delisting
This solution walks you through confirming your mail server's DNS settings and contacting Microsoft 365 support to remove your IP from the block list.
Error S3150 is a strict block-list issue on Microsoft's end, meaning standard DNS propagation alone will not resolve the problem. Manual intervention via a Microsoft support ticket is required.
Check your domain's SPF, A, and reverse-DNS (PTR) records using a DNS lookup tool to ensure they correctly point to your new server IP.
Have your Microsoft 365 tenant administrator log in to the Microsoft 365 admin center using their administrator credentials.
Navigate to the 'Support' section and select 'New service request'. Provide the bounce message details, including the S3150 error code and the blocked IP address.
Explicitly request remediation or delisting for the sending IP. Microsoft support will review the request and remove the block if the IP meets their sender reputation guidelines.
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Frequently Asked Questions
What does bounce error S3150 mean in Outlook and Hotmail?
Error S3150 means that the IP address of your sending mail server has been flagged and placed on a Microsoft block list, causing their servers to automatically reject your emails.
Why is my new IP address blocked by Microsoft?
New IP addresses often lack an established sending reputation, or they may have been previously used for spam by a former owner. Microsoft proactively blocks these IPs to protect their users until the new owner proves legitimacy.
Will waiting for DNS propagation fix the S3150 error?
No. While correctly configuring and propagating your SPF, DKIM, and reverse-DNS records is a mandatory prerequisite, you must still manually request IP delisting from Microsoft to clear the S3150 error.
