module_template.module

<?php

/**
 * @file
 * module_template.module.
 */

use Drupal\Core\Render\Markup;

/**
 * Implements hook_toolbar_alter().
 */
function module_template_toolbar_alter(&$items) {
  /* Añado iconos a la toolbar de administración */
  $items['administration']['#attached']['library'][] = 'module_template/toolbar';
}

/**
 * Implements hook_page_attachments().
 */
function module_template_page_attachments(array &$attachments) {
  /* Añadir el CSS y JS a toda la web */
  $attachments['#attached']['library'][] = 'module_template/global_libraries';
}

/**
 * Implements hook_mail().
 */
function module_template_mail(string $key, array &$message, array $params) {
  $config_site = \Drupal::config('system.site');

  /* Cabeceras */
  $message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed; delsp=yes';
  $message['from'] = $config_site->get('name') . '<' . $config_site->get('mail') . '>';

  /* Copias del mensaje */
  if (isset($params['Cc']) and !is_null($params['Cc'])) {
    $message['headers']['Cc'] = $params['Cc'];
  }
  if (isset($params['Bcc']) and !is_null($params['Bcc'])) {
    $message['headers']['Bcc'] = $params['Bcc'];
  }

  /* Datos comunes a todos los envíos */
  $message['reply-to'] = $message['from'];
  $message['subject'] = $params['subject'];
  $message['body'][] = Markup::create($params['message']);

  /* Compruebo si el mensaje tiene adjuntos */
  if (isset($params['attachments'])) {
    /* Solución para los adjuntos duplicados en Outlook. */
    $message['params']['attachments'] = [];

    foreach ($params['attachments'] as $attachment) {
      $message['params']['attachments'][] = [
        'filepath' => $attachment['filepath'],
        'filename' => $attachment['filename'],
        'filemime' => $attachment['filemime'],
      ];
    }
  }
}