MailerHooks.php

<?php

namespace Drupal\mailer\Hook;

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Hook\Attribute\Hook;
use Drupal\Core\StringTranslation\StringTranslationTrait;

/**
 * Hook implementations for mailer.
 */
class MailerHooks {
    use StringTranslationTrait;
    
    /**
     * Implements hook_help().
     */
    public function help($route_name, RouteMatchInterface $route_match) : ?string {
        switch ($route_name) {
            case 'help.page.mailer':
                $output = '';
                $output .= '<h3>' . $this->t('About') . '</h3>';
                $output .= '<p>' . $this->t('The Mailer module provides an experimental API to build and deliver email messages based on Symfony mailer component. For more information, see the <a href=":mailer">online documentation for the Mailer module</a>.', [
                    ':mailer' => 'https://www.drupal.org/docs/core-modules-and-themes/experimental-extensions/experimental-modules/mailer',
                ]) . '</p>';
                return $output;
            default:
                return NULL;
        }
    }

}