JavaMail SMTP错误

Question

我创建了一个简单的在线表单，用于通过电子邮件打包和发送信息。我已经习惯了JavaMail API并设法在之前发送电子邮件，但现在我尝试时收到错误。这是发送我的消息的代码（带有一些与消息正文中的信息有关的细节，因为它不适用于我收到的错误）。

    /**
     * Format the email and send it.
     */
    private void Send()
    {
        this.host = new String("*************");
        this.from = new String(text_emailAddress.getText());
        this.to = new String ("**************");

        this.properties = new Properties();
        this.properties.put("mail.transport.protocol", "smtp");
        this.properties.put("mail.smtp.host", host);
        this.properties.put("mail.smtp.user", "*************");
        this.properties.put("mail.smtp.pass", "*************");
        this.properties.put("mail.smtp.auth", "true");
        this.properties.put("mail.debug", "true");
        this.properties.put("mail.smtp.port", "25");

        this.session = Session.getDefaultInstance(properties);
        this.message = new MimeMessage(session);

        try
        {
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject(*************);

            message.setText(this.messageBody);
            message.setSentDate(new Date());

            MimeMultipart multipart = new MimeMultipart();

            BodyPart attachmentBodyPart = new MimeBodyPart();
            attachmentBodyPart.setText(createMessageText());
            attachmentBodyPart.setFileName(text_customerName.getText() + dateString+".csv");
            multipart.addBodyPart(attachmentBodyPart);

            message.setContent(multipart, "attachment");

            Transport tran = session.getTransport("smtp");
            tran.connect("*************", 25, "*************", "*************");
            message.saveChanges();
            tran.sendMessage(message, message.getAllRecipients());
            tran.close();
            System.out.println("Message Successfully Sent.");
        }
        catch(AddressException ae){     ae.printStackTrace(); }
        catch(MessagingException me){   me.printStackTrace(); }
    }

虽然当我尝试发送邮件时，我收到错误：

javax.mail.MessagingException: Could not connect to SMTP host: *************, port: 25, response: -1

有人知道SMTP服务器的-1响应是什么意思吗？我试过四处寻找，但我似乎无法弄清楚可能导致此错误的原因。这似乎应该可行，并且我使用的IP地址是我在我工作的公司的网络管理员处得到的（尽管它以“10”开头，这听起来并不像外部SMTP地址） 。非常感谢，

• 麦克