JAVA uses port 465 and port 25 to implement the business of sending emails

SMTP service and SMTPS service

1. Scenario introduction (why use SMTPS)

1、SMTP 服务使用明文通信，邮箱账号、密码极易被监听，导致邮箱被盗事件频繁发生、甚至发生泄密事件。
2、SMTPS是SSL/TLS通讯协议的 内容一开始就被保护起来了 是看不到原文的
它继承了SSL安全协议的非对称加密的高度安全可靠性，可防止邮件泄露。
为了加强网络安全管理，所以要使用SMTPS服务进行邮箱业务的完善
3、若只是简单的实现邮箱功能可以使用SMTP服务，若是追求安全性的邮箱业务必须要使用SMTPS服务

2. Preparation work (jar package for business implementation, etc.)

1、使用JAVA发送邮件前需要准备两个JAR包，分别为activation.jar与mail-1.4.7.jar
2、由于是使用SPring的JavaMailSenderImp实现的，所以JDK与Spring这些基础的也要准备好环境

jar package download address

链接：https://pan.baidu.com/s/1DiQDFjCPzc6y85JeZuGf-Q 
提取码：rodb

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3. Use port 25 to simply implement SMTP service (code demonstration)

This time I use 163 mailbox as an example for demonstration.

3.1. First create a public method class

package com.yadong.mailUtil;
import javax.mail.PasswordAuthentication;

class MailAuthenticator extends javax.mail.Authenticator {
    private String strUser;

    private String strPwd;

    public MailAuthenticator(String user, String password) {
        this.strUser = user;
        this.strPwd = password;
    }
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(strUser, strPwd);
    }
}

3.2. Implementation content of the code

package com.yadong.mailUtil;
import java.io.UnsupportedEncodingException;

import java.util.Date;
import java.util.Properties;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMessage.RecipientType;


import org.springframework.mail.javamail.JavaMailSenderImpl;
import org.springframework.mail.javamail.MimeMessagePreparator;


public class MailUtil {
    // 邮件分发器
    public static JavaMailSenderImpl mailSender = new JavaMailSenderImpl();
    //这是发送邮件的标题
    public static String subject = "这是发送邮件的标题";
    //这是发送邮件的内容
    public static String content = "这是发送邮件的内容";
    //这是发送者Email
    public static String fromAddress = "******@163.com";
    //这是发送者的用户名
    public static String smtpUserName = "*********@163.com";
    //163邮箱的授权码，并不是163邮箱的密码，而是开启SMTP服务时给予的授权码
    public static String smtpPassword = "******";
    //接收者Email
    public static String toAddress = "*******@qq.com";
    //SMTP服务器
    public static String ServerFromDB = "smtp.163.com";
    //服务器的端口
    private static String port = "25";

    /**
     * 发送邮件
     *
     * @param subject     标题
     * @param content     内容
     * @param fromAddress 发送者Email
     * @param toAddress   接收者Email
     * @throws Exception
     */
    public static void sendEmail(final String subject, final String content,
                                 final String fromAddress, final String toAddress) throws Exception {

        mailSender.setHost(ServerFromDB);//SMTP服务器
        mailSender.setPort(Integer.parseInt(port));//端口
        Properties props = System.getProperties();
        props.put("mail.smtp.auth", "true");
        MailAuthenticator mailAuth = new MailAuthenticator(smtpUserName, smtpPassword);
        Session session = Session.getInstance(props, mailAuth);
        mailSender.setSession(session);

            final InternetAddress[] mailToAddresses = new InternetAddress[1];
            mailToAddresses[0] = new InternetAddress(toAddress);
            MimeMessagePreparator preparator = new MimeMessagePreparator() {
                public void prepare(MimeMessage mimeMessage)
                        throws MessagingException, UnsupportedEncodingException {
                    mimeMessage
                            .setRecipients(RecipientType.TO, mailToAddresses);
                    InternetAddress ia = new InternetAddress(fromAddress);
                    ia.setPersonal(fromAddress);
                    mimeMessage.setFrom(ia);
                    mimeMessage.setSentDate(new Date());
                    mimeMessage.setSubject(subject);
                    mimeMessage.setText(content);
                }
            };
            mailSender.send(preparator);
        }

    public static void main(String[] args) throws Exception {
        sendEmail(subject,content,fromAddress,toAddress);
        }
    }

4. Use port 465 to implement SMTPS service (code demonstration)

This time, port 465 of the 163 mailbox server is used as an example for demonstration.

4.1. First create a public method class

package com.yadong.mailUtil;
import javax.mail.PasswordAuthentication;

class MailAuthenticator extends javax.mail.Authenticator {
    private String strUser;

    private String strPwd;

    public MailAuthenticator(String user, String password) {
        this.strUser = user;
        this.strPwd = password;
    }
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(strUser, strPwd);
    }
}

4.2. Contents of code implementation

package com.yadong.mailUtil;

import java.io.UnsupportedEncodingException;

import java.util.Date;
import java.util.Properties;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMessage.RecipientType;


import org.springframework.mail.javamail.JavaMailSenderImpl;
import org.springframework.mail.javamail.MimeMessagePreparator;


public class MailUtil {
    // 邮件分发器
    public static JavaMailSenderImpl mailSender = new JavaMailSenderImpl();
    //这是发送邮件的标题
    public static String subject = "这是发送邮件的标题";
    //这是发送邮件的内容
    public static String content = "这是发送邮件的内容";
    //这是发送者Email
    public static String fromAddress = "******@163.com";
    //这是发送者的用户名
    public static String smtpUserName = "********@163.com";
    //163邮箱的授权码，并不是163邮箱的密码，而是开启SMTP服务时给予的授权码
    public static String smtpPassword = "******";
    //接收者Email
    public static String toAddress = "*******@qq.com";
    //SMTP服务器
    public static String ServerFromDB = "smtp.163.com";
    //服务器的端口
    private static String port = "465";

    /**
     * 发送邮件
     *
     * @param subject     标题
     * @param content     内容
     * @param fromAddress 发送者Email
     * @param toAddress   接收者Email
     * @throws Exception
     */
    public static void sendEmail(final String subject, final String content,
                                 final String fromAddress, final String toAddress) throws Exception {

        mailSender.setHost(ServerFromDB);//SMTP服务器
        mailSender.setPort(Integer.parseInt(port));//端口
        Properties props = System.getProperties();
        props.setProperty("mail.smtp.auth", "true");
        props.setProperty("mail.smtp.port", port);
        props.setProperty("mail.smtp.socketFactory.port", port);
        props.setProperty("mail.smtp.socketFactory.fallback", "false");
        props.setProperty("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.setProperty("mail.smtp.ssl.protocols", "TLSv1.2");
        MailAuthenticator mailAuth = new MailAuthenticator(smtpUserName, smtpPassword);
        Session session = Session.getInstance(props, mailAuth);
        mailSender.setSession(session);

            final InternetAddress[] mailToAddresses = new InternetAddress[1];
            mailToAddresses[0] = new InternetAddress(toAddress);
            MimeMessagePreparator preparator = new MimeMessagePreparator() {
                public void prepare(MimeMessage mimeMessage)
                        throws MessagingException, UnsupportedEncodingException {
                    mimeMessage
                            .setRecipients(RecipientType.TO, mailToAddresses);
                    InternetAddress ia = new InternetAddress(fromAddress);
                    ia.setPersonal(fromAddress);
                    mimeMessage.setFrom(ia);
                    mimeMessage.setSentDate(new Date());
                    mimeMessage.setSubject(subject);
                    mimeMessage.setText(content);
                }
            };
            mailSender.send(preparator);
        }

    public static void main(String[] args) throws Exception {
        sendEmail(subject,content,fromAddress,toAddress);
        }
    }

4.3. The difference between SMTP and SMTPS code implementation

//代码的主体并没有变化，而是在properties配置类中增加一些配置，分别为以下配置
        Properties props = System.getProperties();
        props.setProperty("mail.smtp.auth", "true");
        props.setProperty("mail.smtp.port", "465");
        props.setProperty("mail.smtp.socketFactory.port", "465");
        props.setProperty("mail.smtp.socketFactory.fallback", "false");
        props.setProperty("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.setProperty("mail.smtp.ssl.protocols", "TLSv1.2");

5. Errors that may be encountered

5.1、Could not connect to SMTP host: smtp.163.com, port: 465;

5.1.1. Solution 1

Check whether your device can PING the server
1. First open the telnet function of the device
Control Panel (View Mode icon) -> Program And function-》Enable or turn off the window function

Open CMD Enter telnet smtp.163.com 465

If a black window is displayed It means that PING can be connected. If PING cannot be connected, it will show that the link failed

5.1.2. Solution 2

Add configuration

props.setProperty("mail.smtp.ssl.enable", true);
//将smtp.163.com修改为IP地址
props.setProperty("mail.smtp.host", "220.181.12.16"); //smtp.163.com

5.1.3. Solution 2

Modify java.security: Do not use SSL3, TLSv1, TLSv1.1

# dk.tls.disabledAlgorithms=MD5, SSLv3, DSA, RSA keySize < 2048
jdk.tls.disabledAlgorithms=RC4, DES, MD5withRSA, \
    DH keySize < 1024, EC keySize < 224, 3DES_EDE_CBC, anon, NULL, \
    include jdk.disabled.namedCurves

5.2、Unrecognized SSL message, plaintext connection?

5.2.1. Solution 1

检查端口是否正确
检查是否使用的25端口，却是465端口的配置？

5.3、unable to find valid certification path to requested target

5.2.1. Solution 1

1. Import the certificate
Because the SSL 465 port is encrypted https, you need to import the certificate of the mailbox server into the java virtual machine a> environment.
More detailed steps can be viewed Use keytool to import the https certificate into JDK.
The specific path to import the https certificate is as follows: < /span>

1.	从邮箱服务器上下载证书，具体步骤可以参考网页：
https://jingyan.baidu.com/article/e75aca851e0b5f142edac632.html
2.	保存证书到服务器磁盘后，打开cmd命令行窗口，进入到项目使用的java环境的bin目录
3.	在cmd命令行窗口执行如下两条命令：
keytool.exe -importcert -file C:\Users\Administrator\Desktop\163.cer -keystore  F:\Java\jdk1.8.0_171\jre\lib\security\cacerts -storepass changeit -alias 163.cer

keytool.exe -importcert -file C:\Users\Administrator\Desktop\163.cer -keystore   F:\Java\jdk1.8.0_171\jre\lib\security\jssecacerts -storepass changeit -alias 163.cer

其中C:\Users\Administrator\Desktop\youjianbuding\163.cer为第一步导出的证书的磁盘路径；
	F:\Java\jdk1.8.0_171\jre\lib\security\cacerts为项目使用的jdk的证书环境。
	-alias 163.cer 为起别名
4.	执行命令后会出现如下提示：是否信任证书。输入Y即可。然后证书就导入java环境成功。

Only a certificate containing the SMTP server address in the DNSName can successfully send emails. If the certificate does not contain the SMTP server address, the email cannot be sent
For details on importing certificates, please view https:// blog.csdn.net/qq_45728838/article/details/128547568?spm=1001.2014.3001.5501