Hotmail Rejection with Error S3150 – Need Guidance

Hello,

We are the owners of the IP range 103.95.50.0/24, and one of our IPs (103.95.50.19) is being blocked when sending emails to Hotmail/Outlook users.

The exact SMTP error we are receiving is:

550 5.7.1 Unfortunately, messages from [103.95.50.19] 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.

What we have already checked:

• Our IP range is registered in SNDS. Currently, there is no negative data shown (no spam complaints, no high trap hits, no throttling).

We are also not receiving any JMRP complaint feedback emails, which indicates there are no user complaints or reports from Outlook.com users.

SPF, DKIM, and DMARC are properly aligned for our domains.

Reverse DNS and forward-confirmed PTR are set correctly.

Problem:

Despite having clean SNDS data, Hotmail/Outlook is rejecting all traffic from this IP with error code S3150.

When we try to submit a delisting request through https://sender.office.com, the portal shows a temporary error and does not allow us to submit the mitigation form.

We have tried multiple browsers and networks, but the issue persists.

Request for Guidance:

Since SNDS shows no negative indicators and JMRP feedback is also clean, we are unsure why the IP is blocked.

Can someone from the Microsoft team or community suggest the right escalation path to resolve this?

Is there an alternative contact point when the sender.office.com portal is not working?

Thank you in advance for your guidance.What we have already checked:

Our IP range is registered in SNDS. Currently, there is no negative data shown (no spam complaints, no high trap hits, no throttling).

We are also not receiving any JMRP complaint feedback emails, which indicates there are no user complaints or reports from Outlook.com users.

SPF, DKIM, and DMARC are properly aligned for our domains.

Reverse DNS and forward-confirmed PTR are set correctly.

Problem:

Despite having clean SNDS data, Hotmail/Outlook is rejecting all traffic from this IP with error code S3150.

When we try to submit a delisting request through https://sender.office.com, the portal shows a temporary error and does not allow us to submit the mitigation form.

We have tried multiple browsers and networks, but the issue persists.

Request for Guidance:

Since SNDS shows no negative indicators and JMRP feedback is also clean, we are unsure why the IP is blocked.

Can someone from the Microsoft team or community suggest the right escalation path to resolve this?

Is there an alternative contact point when the sender.office.com portal is not working?

Thank you in advance for your guidance.

Thanks,

Abhinav Dixit