As I mentioned earlier, there is no UI in Drupal to select which plugin the mail manager should use for sending emails programmatically. It figures it out in the getInstance() method by checking the system.mail configuration object, and more specifically, the interface key inside that (which is an array).
By default, this array contains only one record, that is, 'default' => 'php_mail'. That means that, by default, all emails sent use the plugin with the php_mail ID. In order to get our plugin in the game, we have a few options:
- We can replace this value with our plugin ID, which means that all emails will be sent with our plugin
- We can add a new record with the key in the module_name_key_name format, which means that ...