All Sending IPs Temporarily Rate Limited (451 4.7.650 – IP Reputation) Without Policy Changes

Question

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

Answer 1

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).

Answer 2

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?

Answer 3

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?

Answer 4

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!

Answer 5

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.