diff --git a/README.md b/README.md
index 8b89413..52a556b 100644
--- a/README.md
+++ b/README.md
@@ -10,3 +10,17 @@ mailman_antispam_chain_behaviour: discard
 Mailing-list owners can manage list-specific header matches and select their
 action (`accept`, `discard`, `hold`, or `reject`) from Postorius. The global
 chain is used only when a matching rule has no explicit action.
+
+Existing lists without any header matches can be initialized through the
+Mailman database model by enabling the optional seed operation:
+
+```yaml
+mailman_seed_empty_list_header_matches: true
+mailman_empty_list_header_matches:
+  - header: 'X-Spam-Flag'
+    pattern: '^YES$'
+    action: 'discard'
+```
+
+The operation is idempotent. A list is modified only when its header-match
+collection is empty; lists with one or more existing rules are left untouched.
diff --git a/defaults/main.yml b/defaults/main.yml
index c2a6439..f7dfcf2 100644
--- a/defaults/main.yml
+++ b/defaults/main.yml
@@ -127,6 +127,12 @@ mailman_antispam_header_checks: []
 # 'accept', otherwise 'hold' will be used.
 mailman_antispam_chain_behaviour: "discard"
 
+# Optionally seed list-specific header matches, but only on mailing lists that
+# do not already have any rules. Existing list configuration is never merged
+# with or replaced by these defaults.
+mailman_seed_empty_list_header_matches: false
+mailman_empty_list_header_matches: []
+
 mailman_start_nntp_runner: 'no'
 
 mailman_repository: 'https://gitlab.com/mailman/mailman-suite.git'
@@ -182,5 +188,3 @@ mailman_postorius_cronjob_frequency:
 mailman_postorius_cronjob_special_times:
   - 'quarter_hourly'
   - 'minutely'
-
-
diff --git a/tasks/mailman.yml b/tasks/mailman.yml
index 283d355..c56b0cd 100644
--- a/tasks/mailman.yml
+++ b/tasks/mailman.yml
@@ -33,7 +33,7 @@
         - '{{ mailman_spool_dir }}'
 
     - name: Create the mailman virtualenv. Manually, because python 3.6
-      become: True
+      become: true
       become_user: '{{ mailman_user }}'
       shell: cd '{{ mailman_home }}' && python3 -m venv '{{ mailman_virtualenv_name }}'
       args:
@@ -111,6 +111,47 @@
 
   tags: [ 'mailman', 'mailman_conf' ]
 
+- name: Seed header matches on lists without existing rules
+  block:
+    - name: Create the Mailman administration scripts directory
+      ansible.builtin.file:
+        path: '{{ mailman_conf_dir }}/scripts'
+        state: directory
+        owner: root
+        group: '{{ mailman_user }}'
+        mode: '0750'
+
+    - name: Install the list header matches seed script
+      ansible.builtin.template:
+        src: seed-empty-list-header-matches.py.j2
+        dest: '{{ mailman_conf_dir }}/scripts/seed_empty_list_header_matches.py'
+        owner: root
+        group: '{{ mailman_user }}'
+        mode: '0440'
+
+    - name: Add header matches only to lists without rules
+      become: true
+      become_user: '{{ mailman_user }}'
+      ansible.builtin.command:
+        argv:
+          - '{{ mailman_bindir }}/mailman'
+          - -C
+          - '{{ mailman_conf_dir }}/mailman.cfg'
+          - shell
+          - --run
+          - seed_empty_list_header_matches.apply
+          - --listspec
+          - '^.*'
+      environment:
+        PYTHONPATH: '{{ mailman_conf_dir }}/scripts'
+      register: mailman_seed_header_matches_result
+      changed_when: "'CHANGED ' in mailman_seed_header_matches_result.stdout"
+
+  when:
+    - not ansible_check_mode
+    - mailman_seed_empty_list_header_matches | bool
+    - mailman_empty_list_header_matches | length > 0
+  tags: [ 'mailman', 'mailman_conf', 'mailman_header_matches' ]
 
 - name: Add the maintenance cron jobs
   tags: ['mailman', 'mailman_conf', 'mailman_cron']