List headers
This PR attempts to add all headers checked by the rspamd maillist plugin.
Example of headers:
X-Loop: Silke Hofstra <silke@hofstra.dev>
Precedence: list
List-Id: all <all.enterprise.slxh.eu>
List-Archive: <https://localhost/all>
List-Owner: <mailto:all@enterprise.slxh.eu>
List-Help: <mailto:all@enterprise.slxh.eu?subject=Help>
List-Subscribe: <mailto:all@enterprise.slxh.eu?subject=Please%20add%20me%20to%20this%20list>
List-Unsubscribe: <mailto:all@enterprise.slxh.eu?subject=Please%20remove%20me%20from%20this%20list>
List-Post: <mailto:all@enterprise.slxh.eu>