Request removal from block list 3150

Question

Request removal from block list 3150.

Can you please remove me from the block list as I’m unable to email my partner. Please see details below.

[Moderator note: personal info removed]

Answer 1

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Hi @Matt Yo

I completely understand that you are receiving the "550 5.7.1 S3150" error stating your IP is on a block list and you an not send email to your partner.

Please note that as a forum moderator, I cannot manually unblock IP addresses or make changes to internal filtering systems on your behalf. Our role is limited to providing technical guidance to help you navigate the correct support channels.

To get this resolved, have you already tried submitting a delisting request through the official Outlook.com Deliverability Support portal? You can do so here: https://olcsupport.office.com/

If you have already contacted them and received an automated response stating that your IP or domain is not blocked (yet your emails are still bouncing), we highly recommend replying directly to that automated response.

Replying to the auto-responder actively escalates the case to a human support agent. You can see examples of users successfully escalating and resolving their cases this way in the following Microsoft Q&A thread:

• How to fix mail delivery error?

I hope this information is helpful and that the backend team can clear up this block for you quickly!

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Answer 2

The error indicates that the sending IP address 34.2.94.17 is on a Microsoft block list (S3150). This is enforced at the IP/network level, not per individual mailbox, so removal must be requested by the owner of that IP (typically the email provider or ISP), not by the end user.

To restore mail delivery to Outlook.com/Hotmail recipients:

1. Contact the email provider or Internet service provider that owns IP 34.2.94.17.
2. Provide them the full non-delivery report (NDR), including:
   • Error: 550 5.7.1 ... part of their network is on our block list (S3150)
   • The blocked IP: 34.2.94.17.
3. Ask the provider to:
   • Investigate and remediate any abuse, spam, or compromised systems on their network.
   • Verify they follow Microsoft’s email best practices and authentication guidance.
   • Use Microsoft’s delist/self-service tools where applicable to request removal from the block list.

If the provider confirms the IP is blocked by Microsoft 365/Exchange Online, they can follow the documented delist process:

• For NDRs that include messages like Access denied, banned sending IP [IP1.IP2.IP3.IP4], external senders must use the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com to request removal from the blocked senders list.
• For NDRs that instruct to forward the message to delist@microsoft.com, the sender must email that address with the full NDR and IP so Microsoft can review and respond.

If the block is due to a custom block list at the recipient’s domain (for example, error codes like 5.7.513), the recipient’s email admin must remove the sending IP from their custom block list.

End users cannot directly remove an IP from Microsoft’s block lists; the responsible network or mail system owner must request delisting after ensuring their systems are compliant and not sending unwanted or malicious traffic.

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References:

• External senders - Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors
• Email non-delivery reports and SMTP errors in Exchange Online
• Fix NDR error "550 5.7.1" in Exchange Online
• External senders - Troubleshoot email sent to Microsoft 365
• Allow or block email using the Tenant Allow/Block List