“Swift Mailer 530 debe emitir un comando STARTTLS primero.” Código de respuesta

Swift Mailer 530 debe emitir un comando STARTTLS primero.

//encrytion should be set while using email library
$transport = (new \Swift_SmtpTransport($smtp_server, $smtp_port))
                        ->setUsername($smtp_username)
                        ->setPassword($smtp_password)
                        ->setEncryption('tls');  //important to set encryption here.