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No resolution on Service Request: S775 continues despite no block detected

Pablo Asenzo 0 Reputation points
2026-03-03T11:16:06.21+00:00

Hello,

I am posting this in reference to Service Request regarding ongoing Outlook.com / Hotmail deliverability problems from IP [Moderator note: Personal information removed].

We are consistently receiving the following SMTP response when sending to Outlook.com recipients:

451 4.7.650 The mail server has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://aka.ms/postmaster (S775) [Name=Protocol Filter Agent][AGT=PFA]

Actions already completed:

  • Checked the Microsoft delist portal
  • Delist result: “Nothing was detected to prevent your mail from reaching Outlook.com customers”
  • Opened Microsoft support case: [Moderator note: Personal information removed]
  • Enabled SNDS access for IP [Moderator note: Personal information removed]
  • SNDS currently shows no visible data

Important context:

This is a legitimate business mail server IP

This is not a bulk marketing or spam-sending source

Our outbound mail volume is extremely low, almost negligible

The rejection is therefore difficult to reconcile with the “IP reputation” explanation

Microsoft’s support workflow itself currently displays the notice that they are aware of an issue causing some IPs to be temporarily rejected at higher rates

At this point, the situation appears contradictory:

The IP is not reported as blocked in Microsoft’s delist system

SNDS provides no actionable telemetry

Yet Outlook.com continues returning S775 temporary rate limiting due to IP reputation

I would appreciate clarification from Microsoft staff on the following points:

Can an IP be affected by S775 reputation-based rate limiting even when it is not listed as blocked in the delist system?

Is this behavior currently associated with the broader Outlook.com temporary rejection issue mentioned in Microsoft’s own support workflow?

If there is no formal block, what specific remediation steps are expected from a sender with very low legitimate volume?

Is there any way to request a manual review of the current reputation/rate-limit state of IP beyond the already opened support case?

Any guidance from Microsoft or from admins who resolved the same condition would be appreciated.

Thank you.

Outlook | Web | Outlook on the web for business | Security
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  1. Tamara-Hu 14,035 Reputation points Microsoft External Staff Moderator
    2026-03-03T15:01:05.5133333+00:00

    Hello @Pablo Asenzo,  

    Thank you for posting your valuable question on the Microsoft Q&A forum.  

    Thank you for posting your question on Microsoft Q&A forum. Please understand that our forum is a public platform, and we will modify your question to cover your personal information including your organization domain name in the description.

    Your personal data will be stored in our private messages and will automatically be deleted after 30 days.

    User's image

    Please notice to hide these personal or organization information next time you post error or some information to protect personal data.

    I'm sincerely sorry for the inconvenience you're experiencing from this issue. 

    Based on your description, I’ve checked my available resources but could not find any official Microsoft incident report or advisory related to this issue at this time. However, several other users have recently reported experiencing similar issue at All Sending IPs Temporarily Rate Limited (451 4.7.650 – IP Reputation) Without Policy Changes

    These widespread reports strongly indicate that this problem is likely caused by a Microsoft-side filtering change or backend reputation system update, rather than an issue with your configuration.  

    Based on the most helpful solution shared by users, here are the recommended steps to resolve the issue: 

    • Submit a support ticket through the OLC Support Portal: https://olcsupport.office.com/ 
    • When Microsoft replies “No issues detected,” respond and request escalation 
    • Wait for the escalation result 
      • Approximately 23 hours after requesting escalation, Microsoft responded with: 
      • “The connection and throttling limitation against your IP has been set to a more appropriate level based on your reputation.” 
    • Delivery should resume within 1–2 hours 

    If you've already submitted a support request from this channel, you can try reaching out to Microsoft Technical Support Team for official guidance and confirmation about this issue:

    For Business/Education Support: If you purchase your product directly from Microsoft: 

    1.Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support    

    2.Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn .  

    Or you can follow these steps: 

    • Sign in to the Microsoft 365 Admin Center at admin.cloud.microsoft. 
    • On the right side of the screen, select the Help & Support button.  사용자의 이미지
    • In the pane that opens, switch the “Support Assistance” toggle to OFF. 
    • A description field will appear - clearly explain your issue in the “How can we help?” box.  User's image
      • Click Get Help to submit and create your support request. 

    If you purchase your product from a partner or reseller: Contact the reseller's support provider to help open a service request on behalf of you instead.    

    Microsoft Technical Support Team can perform deeper diagnostics and, if needed, escalate the case to the appropriate internal team for further analysis. This ensures the issue is formally tracked and may contribute to a future fix.   

    Please let me know if you need any further assistance. Thank you for reaching out! 

    If you have extra questions about this answer, please click "Comment". 

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

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