mailman

The site-wide antispam defaults are deliberately empty:

mailman_antispam_header_checks: []
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:

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.