/**
 * Implements hook_mail().
 */
function {{ machine_name }}_mail($key, &$message, $params) {
  $account = $params['account'];
  $context = $params['context'];
  $variables = [
    '%site_name' => \Drupal::config('system.site')->get('name'),
    '%username' => $account->getDisplayName(),
  ];
  if ($context['hook'] == 'taxonomy') {
    $entity = $params['entity'];
    $vocabulary = Vocabulary::load($entity->id());
    $variables += [
      '%term_name' => $entity->name,
      '%term_description' => $entity->description,
      '%term_id' => $entity->id(),
      '%vocabulary_name' => $vocabulary->label(),
      '%vocabulary_description' => $vocabulary->getDescription(),
      '%vocabulary_id' => $vocabulary->id(),
    ];
  }

  // Node-based variable translation is only available if we have a node.
  if (isset($params['node'])) {
    /** @var \Drupal\node\NodeInterface $node */
    $node = $params['node'];
    $variables += [
      '%uid' => $node->getOwnerId(),
      '%url' => $node->url('canonical', ['absolute' => TRUE]),
      '%node_type' => node_get_type_label($node),
      '%title' => $node->getTitle(),
      '%teaser' => $node->teaser,
      '%body' => $node->body,
    ];
  }
  $subject = strtr($context['subject'], $variables);
  $body = strtr($context['message'], $variables);
  $message['subject'] .= str_replace(["\r", "\n"], '', $subject);
  $message['body'][] = MailFormatHelper::htmlToText($body);
}