So let's start by creating our Mail plugin class, and if you remember, plugins go inside the Plugin folder of our module namespace. Mail plugins belong inside a Mail folder. So this is what a simple skeleton mail plugin class can look like:
namespace Drupal\hello_world\Plugin\Mail;use Drupal\Core\Mail\MailFormatHelper;use Drupal\Core\Mail\MailInterface;use Drupal\Core\Plugin\ContainerFactoryPluginInterface;use Symfony\Component\DependencyInjection\ContainerInterface;/** * Defines the Hello World mail backend. * * @Mail( * id = "hello_world_mail", * label = @Translation("Hello World mailer"), * description = @Translation("Sends an email using an external API specific to our Hello World module.") * ) */class HelloWorldMail implements ...
