diff --git a/CHANGELOG.md b/CHANGELOG.md
index b39f60d8..490848c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,7 +22,8 @@ All notable changes to this project will be documented in this file. The format
   - Bump version to [1.1.0](https://github.com/fail2ban/fail2ban/releases/tag/1.1.0). For more information, check the [changelog](https://github.com/fail2ban/fail2ban/blob/1.1.0/ChangeLog).
 - **Documentation:**
   - Rewritten and organized the pages for Account Management and Authentication ([#4122](https://github.com/docker-mailserver/docker-mailserver/pull/4122))
-
+- **Postfix**
+  - Disable Microsoft reactions to outgoing mail. ([#4120](https://github.com/docker-mailserver/docker-mailserver/pull/4120))
 
 #### Fixes
 
diff --git a/target/postfix/sender_header_filter.pcre b/target/postfix/sender_header_filter.pcre
index cc0a79ab..fe4ff045 100644
--- a/target/postfix/sender_header_filter.pcre
+++ b/target/postfix/sender_header_filter.pcre
@@ -8,4 +8,4 @@
 /^\s*X-Mailer/                      IGNORE
 /^\s*X-Originating-IP/              IGNORE
 /^\s*Received: from.*127.0.0.1/     IGNORE
-
+/^Content-Type:/i                   PREPEND X-MS-Reactions: disallow