Symfony mailer component added as a composer dependency

The Symfony mailer component has been added as a composer dependency. All supported transports are accessible via an experimental mail plugin which can act as a drop-in replacement for the existing default php mail plugin.

Administrators may switch to the new mail plugin using the contrib Mail System module. Or alternatively overriding the config from settings.php:

$config['system.mail']['interface'] = [ 'default' => 'symfony_mailer' ];

In order to configure the transport DSN, specify its components in the mailer_dsn config. The following examples may serve as a starting point:

• For the default sendmail transport:
  

  $config['system.mail']['mailer_dsn'] = [
    'scheme' => 'sendmail',
    'host' => 'default',
  ];
  

• For mailpit on localhost:
  

  $config['system.mail']['mailer_dsn'] = [
    'scheme' => 'smtp',
    'host' => 'localhost',
    'port' => 1025,
  ];
  

• For authenticated SMTP:
  

  $config['system.mail']['mailer_dsn'] = [
    'scheme' => 'smtp',
    'host' => 'smtp.example.com',
    'user' => 'some-username@example.com',
    'password' => 'correct horse battery staple',
    'options' => [
      'local_domain' => 'example.org',
    ],
  ];
  

Note that an initial implementation shipping with Drupal 10.2.0-beta1 specified mailer_dsn as an URI-like string. That form allowed to supply multiple transports in a High Availability or Load Balancing configuration. From Drupal 10.2.0-beta2 onwards, those advanced use cases are not supported anymore out-of-the-box. In return, the configuration of the standard case becomes much simpler.