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Microsoft Defender for Office 365 Blog
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Strengthening Email Ecosystem: Outlook’s New Requirements for High‐Volume Senders

Puneeth's avatar
Puneeth
Icon for Microsoft rankMicrosoft
Apr 02, 2025

This applies to Outlook.com - our consumer service, which is supporting hotmail.com live.com and outlook.com consumer domain addresses.

April 29th Update - Changes have been made to the action take on messages that do not meet requirements, please see details below. Introduction In an era where email remains one of the most widel...
Updated Apr 30, 2025
Version 4.0
awareness & training
email protection basics
Truusje's avatar
Truusje
Occasional Reader
Mar 12, 2026

Help needed with the 550 5.7.515 error. Received a message from my meanwhile previous provider that my mail-account was used to send spam, that a 'problem' occured with their server and a 'corrupted' backup. All happened without my knowledge. 
Moved to another provider. Problem seems solved. I can send to personal Microsoft accounts again for example. But business clients that have hosted their e-mail at Microsoft still can't receive my mail although my new provider says that they are delivered.
An error message isn't received anymore. Putting my account on the 'safe mail' list doesn't help (as read in the article above).

We're groping in the dark now; does someone have an answer?
Lots of thanks in advance!