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Dear Microsoft Outlook Postmaster Team,
I am reaching out regarding an ongoing issue with one of our mail server IPs: XXX.XX.XXX.XX. We are currently receiving the following error when attempting to send emails to Outlook/Hotmail users: 550 5.7.1 Unfortunately, messages from [XXX.XX.XXX.XX] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). We have submitted delisting requests via both https://olcsupport.office.com/ and https://sender.office.com/, which reported successful processing or no active blocks. However, the issue persists, and messages continue to be rejected with the same S3150 block error. We take deliverability and sender reputation seriously. Here are the steps we have taken: - SPF, DKIM, and DMARC are properly configured and passing authentication checks. - We only send to opt-in recipients and maintain strict list hygiene. - Bounce handling and unsubscribe mechanisms are in place. - The volume of emails is being throttled, and no spam campaigns have been sent. We kindly request a review of the IP reputation for XXX.XX.XXX.XX and assistance in resolving the S3150 block. If there are any additional remediation steps required from our side, we are ready to comply. Thank you for your time and support.
Using New Outlook on Windows for personal email, calendar, and contact management
Locked Question. This question was migrated from the Microsoft Support Community. You can vote on whether it's helpful, but you can't add comments or replies or follow the question.
Hi,
It has been a while and I am writing to see how things are going with this issue. Have you had a chance to check the replies provided? Any update would be appreciated.
We appreciate your patience and are here to help. Looking forward to your response.
Best regards
Henry-N - MSFT | Microsoft Community Support Specialist
Hi,
Thank you for posting on Microsoft Community.
I sent you a Private Message with PII related. Could you kindly check your Private Message and check if my solution provided help you resolve your issue.
Here are the steps to open View Private Messages:
To view private email options, sign in to Microsoft Community> use the email account that posted this thread information to Microsoft Community> > click Profile in the upper-right corner, and then select My Profile.
Thank you for patience and understanding.
Best Regards,
Henry N-MSFT | Microsoft Community Support Specialist