MailInterface

class \Drupal\Core\Mail\Plugin\Mail\PhpMail implements \Drupal\Core\Mail\MailInterface
class \Drupal\Core\Mail\Plugin\Mail\SymfonyMailer implements \Drupal\Core\Mail\MailInterface, \Drupal\Core\Plugin\ContainerFactoryPluginInterface
class \Drupal\Core\Mail\Plugin\Mail\TestMailCollector extends \Drupal\Core\Mail\Plugin\Mail\PhpMail implements \Drupal\Core\Mail\MailInterface