/^From: (.*)/    WARN From Header: $1
/^To: (.*)/    WARN To Header: $1
/^Cc: (.*)/ WARN Cc Header: $1

header_checks = pcre:/etc/postfix/header_checks.pcre

Headers are logged like this

From: aaa@hogehoge.com
To: bbb@hoge.jp
Cc: ccc@hogehoge.com

2025-03-02T10:41:31.581092+09:00 mail postfix/cleanup[1060]: 75B1DA03B5: warning: header From: "aaa@hogehoge.com" <aaa@hogehoge.com> from hoge.hogehoge.com[xx.xxx.xx.xx]; from=<aaa@hogehoge.com> to=<bbb@hoge.jp> proto=ESMTP helo=<hoge.hogehoge.com>: From Header: "aaa@hogehoge.com" <aaa@hogehoge.com>
2025-03-02T10:41:31.581236+09:00 mail postfix/cleanup[1060]: 75B1DA03B5: warning: header To: =?iso-2022-jp?B?GyRCPy5MbxsoQiAbJEI+PjBmGyhC?= <bbb@hoge.jp> from hoge.hogehoge.com[xx.xx.xx.xx]; from=<aaa@hogehoge.com> to=<bbb@hoge.jp> proto=ESMTP helo=<hoge.hogehoge.com>: To Header: =?iso-2022-jp?B?GyRCPy5MbxsoQiAbJEI+PjBmGyhC?= <bbb@hoge.jp>
2025-03-02T10:41:31.581360+09:00 mail postfix/cleanup[1060]: 75B1DA03B5: warning: header CC: "ccc@hogehoge.com" <ccc@hogehoge.com> from hoge.hogehoge.com[xx.xx.xx.xx]; from=<aaa@hogehoge.com> to=<bbb@hoge.jp> proto=ESMTP helo=<hoge.hogehoge.com>: Cc Header: "ccc@hogehoge.com" <ccc@hogehoge.com>

Add the following to /etc/postfix/maps/sender_header_filter.pcre

/^From: (.*)/    WARN From Header: $1
/^To: (.*)/    WARN To Header: $1
/^Cc: (.*)/ WARN Cc Header: $1

smtp_header_checks = pcre:/etc/postfix/maps/sender_header_filter.pcre

For 04 Docker MailServer

docker-compose cp mailserver:/etc/postfix/maps/sender_header_filter.pcre ./docker-data/dms/config/

    volumes:
      - ./docker-data/dms/config/header_checks.pcre:/etc/postfix/header_checks.pcre
      - ./docker-data/dms/config/sender_header_filter.pcre:/etc/postfix/maps/sender_header_filter.pcre

header_checks = pcre:/etc/postfix/header_checks.pcre

Verify that both settings are included:

• header_checks (receiving)
• smtp_header_checks (sending)

# docker-compose exec mailserver grep header_checks /etc/postfix/main.cf
header_checks = pcre:/etc/postfix/header_checks.pcre
smtp_header_checks = pcre:/etc/postfix/maps/sender_header_filter.pcre

# docker-compose up -d --force-recreate