I’m converting a plugin to OOP using boilerplate, and I want to clean up the code.

• In the construct part of “class-plugin.php” I’m able set $this->my_mailer();

• In load_dependencies() I include “class-my-mailer.php” and pass it to the loader.

  // class-plugin.php        
  public function __construct() {
    ...
    $this->load_dependencies();
    $this->set_locale();
    $this->define_admin_hooks();
    $this->define_public_hooks();     
    $this->my_mailer();
  }
  
  private function load_dependencies() {
    ...
    require_once plugin_dir_path( dirname( __FILE__ ) ) . 'includes/class-my-mailer.php';
  }
  
  public function my_mailer() {
    $my_mail = new My_Mailer();
    // test sending mail on load
    // $this->loader->add_action( 'init', $my_mail, 'send_mail' ); // callback needed
  }
  

I see the solution using a callback method. What I’m trying to accomplish is to use $my_mail->send_mail(‘tosomeone@world.com’); where necessary. WordPress keep saying the variable $my_mail does not exist.
Can someone please show me the right way to do this, or point me in the right direction?