Other people have good answers above, but I wanted to add a note on my experience here. I've found that when using Gmail as an outbound SMTP server for my webapp, Gmail only lets me send ~10 or so messages before responding with an anti-spam response that I have to manually step through to re-enable SMTP access. The emails I was sending were not spam, but were website "welcome" emails when users registered with my system. So, YMMV, and I wouldn't rely on Gmail for a production webapp. If you're sending email on a user's behalf, like an installed desktop app (where the user enters their own Gmail credentials), you may be okay.

此外，如果你使用Spring，这里有一个使用Gmail进行出站SMTP的工作配置:

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="defaultEncoding" value="UTF-8"/>
    <property name="host" value="smtp.gmail.com"/>
    <property name="port" value="465"/>
    <property name="username" value="${mail.username}"/>
    <property name="password" value="${mail.password}"/>
    <property name="javaMailProperties">
        <value>
            mail.debug=true
            mail.smtp.auth=true
            mail.smtp.socketFactory.class=java.net.SocketFactory
            mail.smtp.socketFactory.fallback=false
        </value>
    </property>
</bean>

Other people have good answers above, but I wanted to add a note on my experience here. I've found that when using Gmail as an outbound SMTP server for my webapp, Gmail only lets me send ~10 or so messages before responding with an anti-spam response that I have to manually step through to re-enable SMTP access. The emails I was sending were not spam, but were website "welcome" emails when users registered with my system. So, YMMV, and I wouldn't rely on Gmail for a production webapp. If you're sending email on a user's behalf, like an installed desktop app (where the user enters their own Gmail credentials), you may be okay.

此外，如果你使用Spring，这里有一个使用Gmail进行出站SMTP的工作配置:

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="defaultEncoding" value="UTF-8"/>
    <property name="host" value="smtp.gmail.com"/>
    <property name="port" value="465"/>
    <property name="username" value="${mail.username}"/>
    <property name="password" value="${mail.password}"/>
    <property name="javaMailProperties">
        <value>
            mail.debug=true
            mail.smtp.auth=true
            mail.smtp.socketFactory.class=java.net.SocketFactory
            mail.smtp.socketFactory.fallback=false
        </value>
    </property>
</bean>

我的完整代码如下所示，运行良好:

package ripon.java.mail;
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;

public class SendEmail
{
public static void main(String [] args)
{    
    // Sender's email ID needs to be mentioned
     String from = "test@gmail.com";
     String pass ="test123";
    // Recipient's email ID needs to be mentioned.
   String to = "ripon420@yahoo.com";

   String host = "smtp.gmail.com";

   // Get system properties
   Properties properties = System.getProperties();
   // Setup mail server
   properties.put("mail.smtp.starttls.enable", "true");
   properties.put("mail.smtp.host", host);
   properties.put("mail.smtp.user", from);
   properties.put("mail.smtp.password", pass);
   properties.put("mail.smtp.port", "587");
   properties.put("mail.smtp.auth", "true");

   // 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("This is the Subject Line!");

      // Now set the actual message
      message.setText("This is actual message");

      // Send message
      Transport transport = session.getTransport("smtp");
      transport.connect(host, from, pass);
      transport.sendMessage(message, message.getAllRecipients());
      transport.close();
      System.out.println("Sent message successfully....");
   }catch (MessagingException mex) {
      mex.printStackTrace();
   }
}
}

嗨，试试这个代码....

package my.test.service;

import java.util.Properties;

import javax.mail.Authenticator;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Message;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class Sample {
    public static void main(String args[]) {
        final String SMTP_HOST = "smtp.gmail.com";
        final String SMTP_PORT = "587";
        final String GMAIL_USERNAME = "xxxxxxxxxx@gmail.com";
        final String GMAIL_PASSWORD = "xxxxxxxxxx";

        System.out.println("Process Started");

        Properties prop = System.getProperties();
        prop.setProperty("mail.smtp.starttls.enable", "true");
        prop.setProperty("mail.smtp.host", SMTP_HOST);
        prop.setProperty("mail.smtp.user", GMAIL_USERNAME);
        prop.setProperty("mail.smtp.password", GMAIL_PASSWORD);
        prop.setProperty("mail.smtp.port", SMTP_PORT);
        prop.setProperty("mail.smtp.auth", "true");
        System.out.println("Props : " + prop);

        Session session = Session.getInstance(prop, new Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(GMAIL_USERNAME,
                        GMAIL_PASSWORD);
            }
        });

        System.out.println("Got Session : " + session);

        MimeMessage message = new MimeMessage(session);
        try {
            System.out.println("before sending");
            message.setFrom(new InternetAddress(GMAIL_USERNAME));
            message.addRecipients(Message.RecipientType.TO,
                    InternetAddress.parse(GMAIL_USERNAME));
            message.setSubject("My First Email Attempt from Java");
            message.setText("Hi, This mail came from Java Application.");
            message.setRecipients(Message.RecipientType.TO,
                    InternetAddress.parse(GMAIL_USERNAME));
            Transport transport = session.getTransport("smtp");
            System.out.println("Got Transport" + transport);
            transport.connect(SMTP_HOST, GMAIL_USERNAME, GMAIL_PASSWORD);
            transport.sendMessage(message, message.getAllRecipients());
            System.out.println("message Object : " + message);
            System.out.println("Email Sent Successfully");
        } catch (AddressException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (MessagingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

这就是我所做的，当我想发送带有附件的电子邮件时，工作正常。：）

 public class NewClass {

    public static void main(String[] args) {
        try {
            Properties props = System.getProperties();
            props.put("mail.smtp.starttls.enable", "true");
            props.put("mail.smtp.host", "smtp.gmail.com");
            props.put("mail.smtp.auth", "true");
            props.put("mail.smtp.port", "465"); // smtp port
            Authenticator auth = new Authenticator() {

                @Override
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication("username-gmail", "password-gmail");
                }
            };
            Session session = Session.getDefaultInstance(props, auth);
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress("username-gmail@gmail.com"));
            msg.setSubject("Try attachment gmail");
            msg.setRecipient(RecipientType.TO, new InternetAddress("username-gmail@gmail.com"));
            //add atleast simple body
            MimeBodyPart body = new MimeBodyPart();
            body.setText("Try attachment");
            //do attachment
            MimeBodyPart attachMent = new MimeBodyPart();
            FileDataSource dataSource = new FileDataSource(new File("file-sent.txt"));
            attachMent.setDataHandler(new DataHandler(dataSource));
            attachMent.setFileName("file-sent.txt");
            attachMent.setDisposition(MimeBodyPart.ATTACHMENT);
            Multipart multipart = new MimeMultipart();
            multipart.addBodyPart(body);
            multipart.addBodyPart(attachMent);
            msg.setContent(multipart);
            Transport.send(msg);
        } catch (AddressException ex) {
            Logger.getLogger(NewClass.class.getName()).log(Level.SEVERE, null, ex);
        } catch (MessagingException ex) {
            Logger.getLogger(NewClass.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

}

当您需要在同一个JVM中任意位置设置多个SMTP会话时，所发布的代码解决方案可能会导致问题。

JavaMail FAQ建议使用

Session.getInstance(properties);

而不是

Session.getDefaultInstance(properties);

因为getDefault只会使用第一次调用时给出的属性。以后对默认实例的所有使用都将忽略属性更改。

见http://www.oracle.com/technetwork/java/faq - 135477. # getdefaultinstance html