outlook cannot receive email

Since your question is in English, I'd like to reply in English for clarity. Thank you for your understanding!

Dear @xukun,

Good day! Welcome to Microsoft Q&A forum!

Based on your description, I understand that your Outlook account has been unable to receive emails since around 1:00 AM UTC+8 on August 5. Senders are receiving a 451 4.7.650 error indicating that the sending mail server IPs have been temporarily rate-limited due to IP reputation, and you would like assistance investigating and removing the restriction.

According to the error provided, 451 4.7.650 "The mail server has been temporarily rate limited due to IP reputation" is typically a temporary restriction applied by Microsoft's filtering systems. This generally indicates that the sending IP address has triggered reputation-based protections due to factors such as sending volume, mail content, recipient engagement, or other sending patterns that Microsoft considers potentially suspicious. It does not necessarily mean the IP is permanently blocked.

To understand the situation better and provide you with the most suitable support, could you confirm the following information: 

• Could you confirm whether the affected mailbox is an Outlook.com (personal) account or a Microsoft 365/Exchange Online (work or school) account?
• Is the issue affecting all incoming emails or only messages from specific senders/domains?
• Have there been any recent changes to the sending mail environment (mail servers, IP addresses, DNS records, or email security configuration)?

Your confirmation would be very helpful in receiving suitable support!

If you're using a work/school account and the affected IP address belongs to your organization, I recommend submitting a delisting request through https://olcsupport.office.com/. If you are not the IT administrator, please contact your IT administrator or email service provider so they can review the issue and submit the request on your behalf.

If you are using Microsoft 365 services, your Microsoft 365 administrator can also open a support case through the Microsoft 365 Admin Center. This will allow the appropriate support team to investigate the mail flow behavior in greater detail.

For more details, you could refer to this article: Get support for Microsoft 365 for business 

Please also note that Microsoft does not currently provide a dedicated tool for checking IP reputation. If needed, you may use reputable third-party IP reputation checking services to assess the health of the sending IP address. As these tools are not operated by Microsoft, please evaluate their findings and recommendations carefully.

Thank you for your kindness and understanding!

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

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那个发件方不是Outlook.com邮箱吧？