Enviar email sob servidor de proxy

Properties properties = System.getProperties();
        properties.put("mail.smtp.auth", "true");
        Session session = Session.getDefaultInstance(properties, null);
        session.setDebug (true);
        message = new MimeMessage(session);
        try {
            message.setContent(text, "text/html");
            message.setSentDate(new Date());
            message.setSubject(subject);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
           
            MimeBodyPart messageBodyPart = new MimeBodyPart();
           
            messageBodyPart.setText(text);
           
            Multipart multipart = new MimeMultipart();
            multipart.addBodyPart(messageBodyPart);
            if(!files.isEmpty()){
                DataSource source;
                for(String path: files){
                    messageBodyPart = new MimeBodyPart();
                    source = new FileDataSource(path);
                    messageBodyPart.setDataHandler(new DataHandler(source));
                    messageBodyPart.setFileName(path); //falta
                    multipart.addBodyPart(messageBodyPart);
                }
            }
            message.setContent(multipart);
            transport = session.getTransport("smtp");
            transport.connect(host, login, senha);
        } catch (MessagingException ex) {
            ex.printStackTrace();
            return new PersonalError("MessagingException", "Problemas com as configurações do email");
        }