Outlook.com (Hotmail) rejects emails from university server with 451 4.7.650 IP reputation error

Question

I am using a private Outlook.com / Hotmail account (@hotmail.de).

Emails sent to me from my university domain (@uni-mainz.de/unimedizin-mainz.de) are not being delivered properly. The sender receives the following delivery status notification:

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

The message indicates that the sending server is being blocked or throttled by Microsoft due to IP reputation issues.

Important points:

• My mailbox is not full.

My account is not restricted or suspended.

Emails from other domains (e.g., Gmail) are delivered without issues.

• The issue only affects emails coming from the university/medical center mail server.

Could you please clarify:

Is this a temporary rate limit?

What is required for the sending server to be delisted?

Is there anything I can do from the recipient side to allow these emails?

Thank you

Answer 1

da du deine frage in der deutschsprachigen community gestellt hast, antworte ich auf deutsch:

bitte verwende dein ms-konto nur zur kommunikation mit microsoft und anmeldung an microsoft-diensten.

für alle anderen zwecke benutze entweder die mail-adresse deines internet-providers oder eines freemailers (gmail/gmx/web etc.)

Answer 2

Hello,

This issue has nothing to do with your account. There's nothing you can do to fix on your end.

The issue needs to be fixed by the university's IT. The IP range their mail server is on has a poor reputation, this can happen if many spam activities are detected from that range of IP addresses, hence email server on the receiving end can reject them. This is quite common industrial practice. Your unversity IT should know what to do. They have to work with their mail service provider to address the issue.