Java发送电子邮件无一例外

Question

尝试使用Java发送电子邮件。从以下位置查找示例：https://www.codejava.net/java-ee/javamail/send-e-mail-in-html-format-using-javamail-api。

但是，尝试发送电子邮件时，代码似乎停留在Transport.send(msg);上，并且没有任何进展。而且也没有超时。

import java.util.Date;
import java.util.Properties;

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

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class HtmlEmailSender {

    public void sendHtmlEmail(String host, String port,
                              final String userName, final String password, String toAddress,
                              String subject, String message) throws AddressException,
        MessagingException {

        // sets SMTP server properties
        Properties properties = new Properties();
        properties.put("mail.smtp.host", host);
        properties.put("mail.smtp.port", port);
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");

        // creates a new session with an authenticator
        Authenticator auth = new Authenticator() {
            public PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(userName, password);
            }
        };

        Session session = Session.getInstance(properties, auth);

        // creates a new e-mail message
        Message msg = new MimeMessage(session);

        msg.setFrom(new InternetAddress(userName));
        InternetAddress[] toAddresses = { new InternetAddress(toAddress) };
        msg.setRecipients(Message.RecipientType.TO, toAddresses);
        msg.setSubject(subject);
        msg.setSentDate(new Date());
        // set plain text message
        msg.setContent(message, "text/html");

        // sends the e-mail
        Transport.send(msg);
        log.info("Success!");

    }

    /**
     * Test the send html e-mail method
     *
     */
    public static void main(String[] args) {
        // SMTP server information
        String host = "smtp.gmail.com";
        String port = "587";
        String mailFrom = "fromemail@gmail.com";
        String password = "password";

        // outgoing message information
        String mailTo = "toemail@gmail.com";
        String subject = "Hello my friend";

        // message contains HTML markups
        String message = "<i>Greetings!</i><br>";
        message += "<b>Wish you a nice day!</b><br>";
        message += "<font color=red>Duke</font>";

        HtmlEmailSender mailer = new HtmlEmailSender();

        try {
            mailer.sendHtmlEmail(host, port, mailFrom, password, mailTo,
                                 subject, message);
            System.out.println("Email sent.");
        } catch (Exception ex) {
            System.out.println("Failed to sent email.");
            ex.printStackTrace();
        }
    }
}

更新： 通过为我的gmail帐户打开IMAP可选项，我摆脱了最初的问题。但是后来我又有了一个例外：

DEBUG: setDebug: JavaMail version 1.6.0
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]
DEBUG SMTP: need username and password for authentication
DEBUG SMTP: protocolConnect returning false, host=smtp.gmail.com, user='myusername', password=<null>
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "smtp.gmail.com", port 587, isSSL true
Failed to sent email.
com.sun.mail.util.MailConnectException: Couldn't connect to host, port: smtp.gmail.com, 587; timeout -1;
  nested exception is:
    java.net.ConnectException: Operation timed out (Connection timed out)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2194)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:726)
    at javax.mail.Service.connect(Service.java:388)
    at javax.mail.Service.connect(Service.java:246)
    at javax.mail.Service.connect(Service.java:195)
    at javax.mail.Transport.send0(Transport.java:254)
    at javax.mail.Transport.send(Transport.java:124)
    at insbot.HtmlEmailSender.sendHtmlEmail(HtmlEmailSender.java:55)
    at insbot.HtmlEmailSender.main(HtmlEmailSender.java:83)
Caused by: java.net.ConnectException: Operation timed out (Connection timed out)
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    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:352)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:238)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2160)
    ... 8 more