postoffice-1.0.x-dev/extensions/postoffice_twig/postoffice_twig.services.yml

services:
  twig.extension.postoffice_twig:
    class: Drupal\postoffice_twig\Template\TwigExtension
    arguments: ['@renderer' ]
    tags:
      - { name: twig.extension }
  postoffice_twig.text_body_subscriber:
    class: \Drupal\postoffice_twig\EventSubscriber\TwigTextBodySubscriber
    tags:
      - { name: event_subscriber }
  postoffice_twig.subject_subscriber:
    class: \Drupal\postoffice_twig\EventSubscriber\TwigSubjectSubscriber
    tags:
      - { name: event_subscriber }
  postoffice_twig.from_subscriber:
    class: \Drupal\postoffice_twig\EventSubscriber\TwigFromSubscriber
    tags:
      - { name: event_subscriber }
  postoffice_twig.reply_to_subscriber:
    class: \Drupal\postoffice_twig\EventSubscriber\TwigReplyToSubscriber
    tags:
      - { name: event_subscriber }