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2026-02-24T07:44:44.0233333+00:00

Hello Microsoft Postmaster Team, 

We are currently experiencing a critical and recurring email delivery issue affecting recipients at outlook.com, live.com, hotmail.com, and msn.com.

All of our sending IPs are returning the following error:

host hotmail-com.olc.protection.outlook.com[52.101.73.3] said: 451 4.7.650 The mail server [X.X.X.X] 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][MxId=11BCD7A8383E2981] [AM1PEPF000252DC.eurprd07.prod.outlook.com 2026-02-24T07:17:38.549Z 08DE6BD4292A78FC] (in reply to MAIL FROM command)

Although the error indicates rate limiting, in practice no emails are being delivered.

Key Points

  • The issue started a few weeks back with one IP then yesterday spread across all IP ranges which spread across EU & US
  • The Microsoft Anti-Spam IP Delist Portal indicates that our IPs are neither listed nor blocked; however, Outlook continues to return 451 4.7.650 reputation-based rate limiting (S775) errors, and after submitting bounce samples, some IPs were unlisted, which suggests there may have been a recent change in Outlook’s filtering or reputation system. Outlook support has not provided any additional details despite repeated follow-ups, and as an ESP, we rely on your assistance and transparency to help resolve this issue and restore normal delivery.
  • In SNDS, all affected IPs show complaint rates below industry standards (<0.3%), with no red status indicators or abnormal spam trap activity. ( hiding the IP list in the screenshot) 
  • We continuously monitor the SNDS portal and promptly process every ARF complaint and spam trap reported by Outlook to maintain and protect our sending reputation.
  • There have been no changes to:
    • Sending patterns/Bounce/ARF volumes 
    • Authentication (SPF, DKIM, DMARC) : We ensure that 100% of our email volume is authenticated with SPF and DKIM, and when a user has not configured DKIM, we apply our default DKIM to maintain full DKIM compliance and align with outlook bulk volume 

We are an established ESP serving millions of users and generating significant legitimate traffic to these affected domains. Historically, we have maintained stable and compliant sending behavior.This issue is actively impacting delivery reliability to Outlook recipients and requires immediate attention. We have already submitted requests through the Outlook delist IP form, but we have not received any resolution or meaningful response, and the rate limiting continues across all affected IPs. 

We are ready to provide our IP ranges and any additional information required to assist with further investigation and troubleshooting.

Recent other external thread around this issues:

https://help.zoho.com/portal/en/community/topic/hotmail-is-blocking-the-zoho-mail-ip

https://learn.microsoft.com/en-za/answers/questions/5776990/ip-reputation-issue

https://learn.microsoft.com/en-us/answers/questions/5778217/not-able-to-send-email-has-been-temporarily-rate-l

Support request:

7098372133 ,7098281425,7098281425,7043152389

Outlook | Web | Outlook.com | Email

  1. 2026-02-25T12:55:12.8033333+00:00

    yeah we got same standard response from microsoft, i provided some more details, and stating the issues was still ongoing, but haven't heard back yet

  2. 2026-02-25T13:36:06.0866667+00:00

    Same Problems here since 25.02.2026.

    Push for visibility.

  3. 2026-02-25T14:13:49.4+00:00

    Same problem, we a using sendgrid with dedicated ip, and problem startet evening 23. february

    451 4.7.650 The mail server [x.x.x.x] has been temporarily rate limited due to IP reputation.

  4. 2026-02-25T14:17:48.86+00:00

    We are experiencing the same issue. It started on the evening of February 23.

    We have tested sending emails using SendGrid and an Ubuntu server with Postfix.

    DMARC, DKIM, and SPF are all passing successfully.

    However, we are receiving the following error:

    451 4.7.650 The mail server [x.x.x.x] has been temporarily rate limited due to IP reputation.

  5. 2026-02-25T14:38:18.5966667+00:00

    We're also seeing this across numerous IPs of shared hosting servers, no obvious spam going out, and very low volume. Asking for delisting and supplying logs seems to have no effect.

  6. 2026-02-25T14:42:36.23+00:00

    Same here. First hit Feb 23 19:53:33 CET

    status=deferred (host eur.olc.protection.outlook.com[x.x.x.x] said: 451 4.7.650 The mail server [x.x.x.x] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://aka.ms/postmaster (S775)

  7. 2026-02-25T14:56:38.73+00:00

    We're experiencing this issue as well.

    Sending from our dedicated /24 Networks. Every Customer is forced to use SPF and DKIM and gradually every of our stacks getting listed.

    We havn't encountered any reputation issues with this networks for years before.

  8. 2026-02-25T15:04:11.3333333+00:00

  9. 2026-02-25T15:04:26.6333333+00:00

  10. 2026-02-25T15:04:52.5933333+00:00

  11. Deleted

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  12. 2026-02-25T15:15:52.16+00:00

    We are also experiencing the same issue.

    Sendgrid, dedicated IP. Exact same error message and timing as the OP.

  13. 2026-02-25T15:34:56.7166667+00:00

    We are also experiencing the same issue.

    Multiple dedicated IPs, spf dkim and dmarc ok

  14. 2026-02-25T15:38:47.6866667+00:00

    We are experiencing the same issue

  15. 2026-02-25T15:39:03.2233333+00:00

    We have the same issue. Error 451 towards Microsoft owned email Services - outlook, live, hotmail etc. The problem started 23rd of February at 07:55.

    Dedicated US SendGrid IP address.

    Only used for OTP-purposes. 99% reputation according to SendGrid. Sending 100k emails per month. No issues for years with the same setup. SPF, DKIM and DMARC is verified and working.

    SupportNo: 7098488186

  16. 2026-02-25T16:10:59.2466667+00:00

  17. 2026-02-25T16:30:09.0966667+00:00

  18. 2026-02-25T16:36:38.69+00:00

    We are experiencing the same issue

  19. 2026-02-25T16:41:38.6133333+00:00

    we are also experiencing this same issue since feb 23

  20. 2026-02-25T16:42:54.3366667+00:00

    we are also experiecing this same issue since feb 23rd

  21. 2026-02-25T16:43:41.95+00:00

    Same problem here, low rate email for 48 hours for outlook.com, live.com, hotmail.com, and msn.com.
    SPF, DKIM and DMARC passed on all online tools
    Ip in any blacklist

  22. 2026-02-25T16:44:51.1333333+00:00

  23. 2026-02-25T16:45:42.34+00:00

  24. 2026-02-25T16:52:49.5833333+00:00

    Dear Microsoft,

    We are currently experiencing the same issue, which began on the evening of February 23.

    Despite this, our mail server is returning the following error message:

    451 4.7.650 – The mail server [x.x.x.x] has been temporarily rate limited due to IP reputation.

    Could you please advise on the potential cause of this rate limiting and the steps we can take to resolve it?

    Thank you for your assistance.

  25. 2026-02-25T16:54:07.0166667+00:00

    Same issue here. Our dedicated server is functioning normally, but emails to Outlook, Hotmail, and Live addresses remain queued and are not being delivered. As a result, new clients are unable to complete registration, which is causing business loss.

    @Microsoft: a prompt resolution would be highly appreciated.

  26. 2026-02-25T17:17:56.39+00:00

    Fix it.

    I hate Microsoft. 😡😡😡😡

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  30. 2026-02-25T17:39:32.1333333+00:00

    We are facing the same issue since Monday 7PM GMT, over 400 emails to microsoft domains deferred / undelivered.

    Is there a global fix from Microsoft or do we have to raise a ticket with OLC Support and pray?

  31. 2026-02-25T17:59:11.0966667+00:00

    I'm also experiencing issues when sending via SendGrid.
    Reported spam level was at 0.01%. We went from nearly 100% delivery to 0%. Thousands of transactional emails.

    I'm assuming SendGrid is also suddenly seeing a high increase with related issues considering they have haphazardly added an article on their support homepage.
    https://support.sendgrid.com/hc/en-usScreenshot 2026-02-25 at 18-58-02 Search For Solutions. Get Support

  32. 2026-02-25T18:32:17.8133333+00:00

    i raised a ticket with OLC and they said everything was fine and i will have no issues sending to them.... having been able to send emails to MS addressess since feb 23

  33. 2026-02-25T18:45:34.51+00:00

    @Brian Appleton make sure you escalate your request. Apparently some people are having success after escalation (though can take over 24 hours).

  34. 2026-02-25T18:47:38.34+00:00

    Is there an escalation channel? or we just reply to same OLC email?

  35. 2026-02-25T18:55:00.4666667+00:00

    My colleague escalated. I asked her how she did it and her response is:

    Yes, just reply back to same email with proper details do not say anything about could be sendgrid issue and all stick to their issue

  36. 2026-02-25T18:57:40.9+00:00

    Thanks Matt. I'll follow that advice and keep the reply focused on their specific issue.

  37. 2026-02-25T19:17:35.9566667+00:00

    Hi everyone, after quite a bit of research and attempts to solve this ourselves, we have reluctantly accepted that we have to wait for MS to respond to our escalated support ticket.

    If we all escalate our tickets, my hope is that MS will fix the problem at its root, rather than dealing with it on a 1 by 1 basis.

    If you submit a ticket and get a standard "everything is fine" response, reply to the email requesting escalation. Don't hint that it could be an issue with your email service provider - at this point, we all know it's not a specific provider, but rather MS itself.

    Good luck

  38. 2026-02-25T20:02:29.9233333+00:00

    Tickets 7098481597 and 7098479295

    In the meantime we have put up a notice not to use Microsoft email addresses (such as Outlook, Hotmail, Live, or MSN) when contacting or registering.

  39. 2026-02-25T20:03:09.1133333+00:00

    Same issue here. Where is Microsoft answers for this? When is this issue notified and solved?

  40. 2026-02-25T20:30:44.07+00:00

  41. 2026-02-25T20:54:44.8066667+00:00

    Our org is also experiencing this issue. Microsoft support has been useless so far.

  42. 2026-02-25T21:05:49.9366667+00:00

    We've been experiencing this since Monday as well. This is a critical problem and I know for a fact that they're aware of it. Whether or not they intend to do anything about it, that I don't know. They could very well be using the "just keep following policy and see if it clears up in a week" strategy, ignoring us because they knew it would cause pushback and committed to deploying the change anyway. But I'm going to keep reaching out and correcting them every time a human responds (the second response I believe).

  43. 2026-02-25T21:58:03.28+00:00

    No reply yet from Microsoft. However, I ran a test and SendGrid is working quickly at the moment. We’re still experiencing issues with Ubuntu Postfix on the other email server.

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  45. 2026-02-25T23:48:19.9033333+00:00

    Our sales team use Outlook via Office 365 Business.

    Last year we implemented Duocircle as our email sender for (only) hotmail emails, as they were getting binned as spam from outlooks email servers.

    Now duocircle is getting delays sending to hotmail emails. Our clients are complaining.

    Its really annoying that Outlook is so bad at routing emails to Hotmail when they are both owned by Microsoft. Now the they are blocking the third party sender we had to implement because of their own ineptitude.

  46. 2026-02-26T00:26:17.16+00:00

    After 48 hours, things are back to normal for me, at least. However, I haven’t received any response to the tickets. Fingers crossed!

  47. 2026-02-26T07:03:09.25+00:00

    Our IP is still being limited. This has been a nightmare. Microsoft...???

  48. Deleted

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  49. 2026-02-26T08:59:32.63+00:00

    As reported by other users, we can confirm that emails are now being accepted by Microsoft, even though there has been no update on the tickets raised. Mail flow is currently back to normal.

    Thank you to everyone in the forum for sharing updates and insights, they were very helpful in tracking the situation. Hopefully, the issue will not recur during peak hours.

  50. 2026-02-26T09:17:54.49+00:00

  51. Volex 5 Reputation points

    2026-02-26T09:24:37.0933333+00:00

    Issue fixed across our mail platform at 22:54 GMT 25/02, 300k+ "451 4.7.650" errors yesterday and 0 since.

  52. 2026-02-26T12:13:32.9466667+00:00

    We had some failed emails delivered late yesterday, but seeing the same deferrals again :-/

    Slightly different error code, 451 4.7.650; but description looks similar.

  53. 2026-02-26T15:28:14.8133333+00:00

    Just got a response from a human at Microsoft and yeah you would have guessed right that they are still in denial ...
    :\

  54. 2026-02-26T16:28:16.8833333+00:00

    Postmaster team acknowledged the issue (https://substrate.office.com/ip-domain-management-snds/Postmaster).

    "We are aware of an issue that may result in certain IP addresses being temporarily rejected at higher rates. We are actively investigating the issue. Please continue to submit tickets if you are experiencing this problem."

  55. 2026-02-27T05:15:52.7033333+00:00

  56. 2026-02-27T09:29:25.8+00:00

    We have the same Issue here.
    Since around 23./24. of February.
    It was fixed for a short while but now its not working again and our IP gets rate limited.

  57. 2026-02-27T13:57:58.13+00:00

    I am having the same issue, emails not sending from this morning (UK) 27/02/26

  58. 2026-02-27T18:56:13.7766667+00:00

    I've also experienced this issue since the 25th. I reported the problem here https://olcsupport.office.com/

    This morning I'm also getting permanent failures:

    <<< 550 5.7.1 Unfortunately, messages from [209.97.222.44] 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. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BCEAB1C9790853] [CH1PEPF0000A34B.namprd04.prod.outlook.com 2026-02-27T17:38:33.025Z 08DE7558E5E8212D]
554 5.0.0 Service unavailable

  59. cc cc 0 Reputation points

    2026-02-28T03:46:26.8633333+00:00

    We use Google Gmail for our email, but several of our customers who are on Microsoft email (Office 365/Exchange) have suddenly stopped receiving messages from us.

    We’ve checked everything on our end:

    • No bounce-backs
    • No delivery failures
    • All authentication (SPF, DKIM, DMARC) is properly configured
    • Our domain and IPs are not on any blacklists
    • Our mail server logs show the emails as successfully delivered

    However, the messages are not appearing in inbox or spam folders on the recipient side.

    We’ve spoken with a few other companies who are experiencing the same issue with Microsoft-hosted email — messages show as delivered with no errors but seem to disappear entirely.

    Has anyone encountered this recently or found a resolution? Any guidance would be greatly appreciated. Our domain is Athena-security.com

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27 answers

  1. 2026-02-25T17:18:48.9266667+00:00

    For what this is worth, we had the exact same issue and noticed it began on 2/23 around 19:00 UTC. I submitted the issue yesterday here https://olcsupport.office.com/, and got a quick reply from Microsoft that no issues were detected. I responded that there are definitely issues and to please escalate.

    Today, around 23 hours after my response, I received another reply from Microsoft that "The connection and throttling limitation against your IP has been set to a more appropriate level based on your reputation." Then about 2 hours after that reply the emails started being accepted by Microsoft (hotmail.com, msn.com, outlook.com, live.com).

  2. 2026-02-25T11:29:52.3166667+00:00

    We have been seeing the same issue on our side since 23 February 2026 at 7:55 PM CET, but it affects only one of several IP addresses. According to SNDS, our complaints rate is below 0.1, and until 23 February, the number of messages sent from our servers to Outlook.com was in the low hundreds per day, as we primarily operate in a B2B environment.

    It would therefore be unusual for a few hundred emails per day to result in a bad reputation for a single IP address—especially considering that our other IPs have similar sending volumes and are not being rate‑limited.

    Additionally, OLC Support has informed us that there are no issues with our IP addresses. We have replied to them stating that the problem persists, but we have not received any follow‑up yet.

    The URL mentioned in the error message (aka.ms/postmaster) is also currently unreachable for us and returns an HTTP 500 error.

    Has anyone here already found a solution, or does anyone have additional ideas on what we can try next?

  3. 2026-02-25T09:34:00.18+00:00

    We are experiencing the exact same issue that people are listing above and it started yesterday.

    We are sending on behalf of several domains using our services and the amount has not changed.

    We have checked our IP against the blacklists tested here: https://mxtoolbox.com/blacklists.aspx and they are all saying "OK".

    Since we are not the only ones experiencing this issue, and the common denominator is Microsoft, when can we expect you to resolve this issue?

  4. 2026-02-25T08:29:12.17+00:00

    We are experiencing the same issue with our server. Our server is used by Estonian Public Libraries to send automated notifications, such as book due date reminders and overdue notices, to patrons. These are critical service messages, sent in batches of dozens or hundreds every morning. It’s vital that these reach our users' Outlook/Hotmail inboxes

    And https://substrate.office.com/ip-domain-management-snds/postmaster/ is not working!

  5. 2026-02-24T22:54:01.3566667+00:00

    We have been throttled since 10AM PT yesterday. Same thing here, we do not allow spam, mass mailing, bulk mailing. Transactional business emails only. All domains have SPF, DKIM, and DMARC setup. Affecting thousands of customers. Emailed MS and they said none of our IPs are listed and we are not blocked. Hopefully it gets resolved soon. We are an email service provider for healthcare professionals.

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