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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
rsetht's avatar
rsetht
Copper Contributor
Jun 27, 2025

Ours are all "Content-Transfer-Encoding: quoted-printable" and still failing DKIM.  

Cdary's avatar
Cdary
Copper Contributor
Jun 28, 2025

Microsoft is experiencing two types of authentication validation issues: the first, consistently reproducible, is DKIM validation of 8-bit bodies or headers; the second, random, is DNS timeouts. It appears you are only affected by the second issue.