Re-add anonymize headers section

docs/u_and_e.md

@@ -15,6 +15,25 @@ mailcow UI configuration parameters can be to...
 
 \* To change SOGos default language, you will need to edit `data/conf/sogo/sogo.conf` and replace "English" by your preferred language.
 
+## Anonymize headers
+
+Save as `data/conf/postfix/mailcow_anonymize_headers.pcre`:
+
+```
+/^\s*Received:[^\)]+\)\s+\(Authenticated sender:(.+)/
+	REPLACE Received: from localhost (localhost [127.0.0.1]) (Authenticated sender:$1
+/^\s*User-Agent/        IGNORE
+/^\s*X-Enigmail/        IGNORE
+/^\s*X-Mailer/          IGNORE
+/^\s*X-Originating-IP/  IGNORE
+/^\s*X-Forward/         IGNORE
+```
+
+Add this to `data/conf/postfix/main.cf`:
+```
+smtp_header_checks = pcre:/opt/postfix/conf/mailcow_anonymize_headers.pcre
+```
+
 ## Backup and restore maildir (simple tar file)
 
 ### Backup