code: public function send()
      {
          $eventManager = $this->getManager()->getEventsManager();
          if ($eventManager) {
              $result = $eventManager->fire('mailer:beforeSend', $this);
          } else {
              $result = true;
          }
  
          if ($result === false) {
              return false;
          }
  
          $this->failedRecipients = [];
  
          //send to queue
          $queue = $this->getManager()->getQueue();
          //$queueName = $this->
  
          if ($this->auth) {
              $queue->putInTube($this->queueName, [
                  'message' => $this->getMessage(),
                  'auth' => $this->smtp,
              ]);
          } else {
              $queue->putInTube($this->queueName, $this->getMessage());
          }
  
          /* $count = $this->getManager()->getSwift()->send($this->getMessage(), $this->failedRecipients);
      if ($eventManager) {
      $eventManager->fire('mailer:afterSend', $this, [$count, $this->failedRecipients]);
      }
      return $count;*/
      }
docs: Send the given Message like it would be sent in a mail client.
  
  All recipients (with the exception of Bcc) will be able to see the other
  recipients this message was sent to.
  
  Recipient/sender data will be retrieved from the Message object.
  
  The return value is the number of recipients who were accepted for
  delivery.
  
  Events:
  - mailer:beforeSend
  - mailer:afterSend
  
  @return int
  
  @see \Swift_Mailer::send()