Troubleshooting Microsoft Delivery Issues & 550 5.7.1 S3140/S3150 Blocks

 

Issue

Emails sent via Twilio SendGrid to Microsoft consumer domains (Outlook.com, Hotmail, MSN, Live.com, etc.) might be blocked and not delivered. The bounce reason usually appears as:
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/S3140) 

This error can appear in delivery logs or bounce notifications. It is driven by Microsoft’s own block lists and reputation systems, and has become especially prevalent following changes to their filtering algorithms.

 

Product

Twilio SendGrid (Email API and/or Marketing Campaigns)

 

Cause

If your account is Free Trial version or under a plan that uses shared IPs

Microsoft can block traffic from shared IPs if they detect poor reputation or suspicious sending patterns across pooled users. Low volume, poor engagement, or inactivity can increase block risk.

If your account is under a plan that uses dedicated IPs

Reputational issues (complaints, sending spikes, inactivity) or missing technical configuration (missing rDNS) can cause blocks. However, recent blocks with S3140/S3150 are most often triggered by Microsoft-side filtering issues, not sender missteps or platform faults.

Important: SendGrid has confirmed with Microsoft that many current blocks (especially S3140/S3150) are not attributable to sender configuration issues or platform problems, but ongoing Microsoft-side changes impacting reputable senders. Microsoft uses tools like SNDS, blocklists, and protocol filters—sometimes erring on the side of over-blocking.

 

Resolution

If your account uses Shared IPs

  1. Increase Sending Volume: If you send less than 1000 emails per month, try to increase your email sending volume, so our system can accurately assess your SendGrid Engagement Quality Score (SEQ) and potentially group your account with better reputation sender pools.
  2. Enable Open tracking: Open tracking must be enabled so our system can assess your Engagement Quality Score. Without it, your engagement data is incomplete.
  3. Track your Engagement Quality Scores: Our system groups senders by engagement quality. Higher SEQ scores increase your chances of being grouped with higher-reputation senders, reducing blocks.
  4. Consider upgrading to a plan with a Dedicated IP: This gives you sole control over the IP reputation and more granular troubleshooting options. Only recommended if your volume supports it, to justify the higher price.

 

 

If your account uses dedicated IPs

  1. Ensure Proper Technical Configuration:
  2. Review Your IP Status in Microsoft SNDS:
    • Log into Microsoft's Smart Network Data Services (SNDS) and check your IP for red flags (e.g. complaints, blocks, spikes). If you have not subscribed to SNDS yet, please follow the steps indicated in the next section. 
  3. Gather Evidence:
    • Using your Email Logs or Email Activity Feed, gather recent bounce/deferral logs displaying the S3140/S3150 block errors.
    • Check your SNDS status. If SNDS shows mostly green results for your IP(s), yet you see a considerable amount of bounces with the S3140/S3150 block errors, you are in a strong position to escalate.
  4. Submit a Delisting and Support Request to Microsoft:
  • Open a ticket through https://olcsupport.office.com. You'll need a Microsoft email for this purpose, but you can use a consumer email (at Outlook.com, Hotmail, MSN, Live.com, etc) without any issue. 
  • Include: sending domain(s), dedicated IP address(es), description of your email program (e.g., transactional, marketing), and recent error messages/bounce codes. Attaching screenshots of the SNDS results will help as well. 
  • Sample request language:
I am requesting an escalation for my deliverability issue.
Sending domain: [your domain]
IP address(es): [your IP(s)]
Description of sending: [e.g., transactional notifications to customers]
Recent error messages: 550 5.7.1 S3140/S3150 block, etc.
  • Microsoft’s initial responses are often automated. Always reply back and specifically request escalation to reach a human agent. Multiple follow-ups may be needed.

 

Additional Information 

 

What is SNDS?

Smart Network Data Services (SNDS) is a reputation portal provided by Microsoft. It allows senders to view data about their IP’s reputation, such as complaint rates and "spamminess" levels (Green/Yellow/Red).


Important: SNDS is a Microsoft-owned service. While Twilio SendGrid can help facilitate access for dedicated IP users, the data and its accuracy are entirely controlled by Microsoft.


Why is Data Sometimes Missing?

It is common for customers to see "No data for specified IPs" or for the data within SNDS to not match SendGrid’s rejection logs. There are two primary reasons for this:

  1. The 100-Message Minimum: Microsoft generally does not display mail traffic or spam data for IPs that sent fewer than 100 messages to Microsoft recipients on a given day. If your volume is low, the dashboard will remain empty.
  2. Reporting Discrepancies: SendGrid reports blocks and bounces in real-time. Microsoft SNDS data is often delayed or aggregated, meaning a block you see in your SendGrid Activity Feed might not appear in the SNDS portal until much later, or at all if the volume threshold wasn't met.

How to Gain SNDS Access:

To view your data, you must request access to your dedicated IP within Microsoft's SNDS Portal.


Option 1: Self-Approval (Recommended for Fast Access): 

You can approve SNDS access yourself and do not need to wait for SendGrid Support. This requires that you have set up rDNS for your dedicated IP.

  • Microsoft allows the owner of the abuse@<your-reverse-DNS-domain> mailbox to grant authority.
  • Submit your access request in the SNDS portal and select the abuse@ address associated with your domain.
  • Monitor that inbox for the authorization email from Microsoft, then click the approval link included.
  • This process completes SNDS access authorization without SendGrid intervention.

Note: You must have an active inbox for abuse@<your-reverse-DNS-domain>. This mailbox is necessary because Microsoft will send an authorization email to this address.


Option 2: SendGrid Courtesy Approval: 

If you cannot use Option 1, SendGrid can manually approve the request as a courtesy.

  • The Address Matters: You must address the request to abuse@sendgrid.com. Requests sent to .net or other aliases will not be received and cannot be approved.
  • 7-Day Expiry: Pending requests now expire after approximately 7 days. If your request has been ongoing longer, you must delete the pending request in the SNDS portal and resubmit it to abuse@sendgrid.com.
  • Verification: To expedite the process with SendGrid Support, provide a screenshot of your Pending Requests table from the SNDS site to confirm the recipient address was selected correctly.

 

Other information

  • Account and Engagement Quality: Information on improving your Engagement Quality Score is available here.
  • Pricing and Upgrades: Learn more about Email API or Marketing Campaign plans on our Pricing and Plans page.
  • Temporary Nature of Microsoft Blocks: Many Microsoft blocks clear themselves over time, especially as reputation signals improve. Retrying after some hours or days may succeed.
  • Twilio SendGrid Ongoing Monitoring: We are monitoring for broader Microsoft reputation changes and will advise as new guidance becomes available.

Need further help? If you need assistance collecting SNDS data, configuring rDNS, or analyzing delivery errors, please reach out to Twilio SendGrid Support.

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