发送邮件错误，javax.mail.MessagingException: 无法连接到 SMTP 主机：localhost，端口：25；

Question

这是我的代码

import java.util.Properties;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;


public class MailSendClass {
    public static void main (String [] args){

      // Recipient's email ID needs to be mentioned.
      String to = "abc82@gmail.com";

      // Sender's email ID needs to be mentioned
      String from = "xyz@gmail.com";

      // Assuming you are sending email from localhost
      String host = "localhost";

      // Get system properties
      Properties properties = System.getProperties();

      // Setup mail server
      properties.setProperty("mail.smtp.host", host);

      // Get the default Session object.
      Session session = Session.getDefaultInstance(properties);

      try{
         // Create a default MimeMessage object.
         MimeMessage message = new MimeMessage(session);

         // Set From: header field of the header.
         message.setFrom(new InternetAddress(from));

         // Set To: header field of the header.
         message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

         // Set Subject: header field
         message.setSubject("Thanks for registering on our website!");

         // Now set the actual message
         message.setText("Welcome To Job Portal !!!!  Again Thanks ");

         // Send message
         Transport.send(message);
         System.out.println("Sent message successfully....");
      }catch (MessagingException mex) {
         mex.printStackTrace();
      }

    }
}

我每次都会收到这个错误

javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25;
  nested exception is:
    java.net.ConnectException: Connection refused: connect
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1706)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:525)
    at javax.mail.Service.connect(Service.java:291)
    at javax.mail.Service.connect(Service.java:172)
    at javax.mail.Service.connect(Service.java:121)
    at javax.mail.Transport.send0(Transport.java:190)
    at javax.mail.Transport.send(Transport.java:120)
    at MailSendClass.main(MailSendClass.java:58)
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:345)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at java.net.Socket.connect(Socket.java:538)
    at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:284)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:227)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1672)
    ... 7 more
BUILD SUCCESSFUL (total time: 3 seconds)

我没有得到为什么会这样的错误。请帮我解决这个错误。

Answer 1

错误是自我解释：javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25;

您在本地主机上没有 SMTP 服务器，但您在那里配置它：

  // Assuming you are sending email from localhost
  String host = "localhost";
  ...
  // Setup mail server
  properties.setProperty("mail.smtp.host", host);

所以你必须：

• 将本地 SMTP 服务器配置为本地系统上的中继（Postfix 或 sendmail 是两个众所周知的服务器）
• 配置一个只跟踪邮件请求但甚至不尝试投递邮件的虚拟服务器（众所周知，Python 有这样的虚拟服务器开箱即用）
• 或使用允许使用的服务器配置您的应用程序 - 在公司环境中联系您的系统管理员，或在个人环境中联系您的 ISP。无论如何，即使是配置真正的继电器，您也需要它。

Answer 2

这是可行的解决方案兄弟。是有保证的

1) 首先打开您要从中发送邮件的 gmail 帐户，例如“xyz@gmail.com”

2) 在下方打开此链接 https://support.google.com/accounts/answer/6010255?hl=en

3) 点击“转到我的帐户中的“安全性较低的应用程序”部分。”选项

4) 然后开机

5）就是这样（：

Answer 3

您应该使用免费的 Google SMTP 服务器作为测试。

mail.host=smtp.gmail.com
mail.username=//your gmail
mail.password=//your password
mail.defaultEncoding=UTF-8
mail.smtp.auth=true
mail.smtp.starttls.required=true
mail.smtp.starttls.enable=true
mail.smtp.socketFactory.class=javax.net.ssl.SSLSocketFactory
mail.smtp.socketFactory.fallback=false
mail.smtp.port=465
mail.smtp.socketFactory.port=465

接下来，使用您的 gmail 登录，然后打开 less secure apps。

Answer 4

你应该看看这两行：

javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25;
Caused by: java.net.ConnectException: Connection refused: connect

错误是：“在 localhost 的 25 端口没有监听”。

您正在尝试使用 localhost:25 作为邮件服务器，但那里没有服务器。

Answer 5

只需使用此提供的解决方案：javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25

并确保在您的 Google 帐户上开启安全性较低的应用访问权限。