Javamail - 无法连接到SMTP主机

我正在尝试从我的java发送电子邮件，但无法连接到我的主机 . 这是我的代码：

public class sendEmail implements Runnable{
     @Override
     public void run(){
        try{
            final String username = "user", password = "pass", from = "from@mail.com", to = "to@mail.com";

            Properties props = new Properties();
            props.setProperty("mail.smtp.user", username);
            props.setProperty("mail.smtp.host", "mail.host.com");
            props.setProperty("mail.smtp.ssl.enable", "true"); 
            props.setProperty("mail.smtp.port", "465");
            props.setProperty("mail.smtp.starttls.enable", "true");
            props.setProperty("mail.smtp.debug", "true");
            props.setProperty("mail.smtp.auth", "true");
            props.setProperty("mail.smtp.socketFactory.port", "465");
            props.setProperty("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
            props.setProperty("mail.smtp.socketFactory.fallback", "false");
            Authenticator auth = new SMTPAuthenticator();
            Session session = Session.getInstance(props, auth);
            session.setDebug(true);

            Message msg = new MimeMessage(session);
            try{
                msg.setSubject("Test SMTP");
                msg.setFrom(new InternetAddress(from));
                msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
                Transport transport = session.getTransport("smtp");
                transport.connect("mail.itbuntuksemua.com", username, password);
                transport.sendMessage(msg, msg.getAllRecipients());
                transport.close();
                System.out.println("Done");
            }catch(MessagingException | NumberFormatException | HeadlessException ex){
                ex.printStackTrace();
            }
        }catch(UnknownHostException | NumberFormatException ex){
            ex.printStackTrace();
        }
     }
 }

在这里我的 SMTPAuthenticator() 代码：

private class SMTPAuthenticator extends javax.mail.Authenticator {
    @Override
    public PasswordAuthentication getPasswordAuthentication() {
        String username = "user"; 
        String password = "pass";
        return new PasswordAuthentication(username, password);
    } 
}

在这里，我的报告错误：

DEBUG：setDebug：JavaMail版本1.4.7 DEBUG：getProvider（）返回javax.mail.Provider [TRANSPORT，smtp，com.sun.mail.smtp.SMTPTransport，Oracle] DEBUG SMTP：useEhlo true，useAuth true DEBUG SMTP：尝试连接到主机“mail.host.com”，端口465，isSSL是真的javax.mail.MessagingException：无法连接到SMTP主机：mail.host.com，端口：465;嵌套异常是：javax.net.ssl.SSLHandshakeException：sun.security.validator.ValidatorException：PKIX路径构建失败：sun.security.provider.certpath.SunCertPathBuilderException：无法在com.sun.mail找到请求目标的有效证书路径.smtp.SMTPTransport.openServer（SMTPTransport.java:1961）位于javax的javax.mail.Service.connect（Service.java:295）的com.sun.mail.smtp.SMTPTransport.protocolConnect（SMTPTransport.java:654） . mail.Service.connect（Service.java:176）at scam.ccChecker $ sendEmail.run（ccChecker.java:186）at java.lang.Thread.run（Thread.java:745）引起：javax.net.ssl .SSLHandshakeException：sun.security.validator.ValidatorException：PKIX路径构建失败：sun.security.provider.certpath.SunCertPathBuilderException：无法在sun.security.ssl.Alerts.getSSLException中找到所请求目标的有效证书路径（Alerts.java： 192）sun.security.ssl.SSLSocketImpl.fatal（SSLSocketImpl.java:1937）at sun.security.ssl.Handshaker.fatalSE（Handshaker.java） ：302）at sun.security.ssl.Handshaker.fatalSE（Handshaker.java:296）at sun.security.ssl.ClientHandshaker.serverCertificate（ClientHandshaker.java:1478）at sun.security.ssl.ClientHandshaker.processMessage（ClientHandshaker . java：212）at sun.security.ssl.Handshaker.processLoop（Handshaker.java:957）at sun.security.ssl.Handshaker.process_record（Handshaker.java:892）at sun.security.ssl.SSLSocketImpl.readRecord（SSLSocketImpl .java：1050）sun.security.ssl.SSLSocketImpl.performInitialHandshake（SSLSocketImpl.java:1363）at sun.security.ssl.SSLSocketImpl.startHandshake（SSLSocketImpl.java:1391）at sun.security.ssl.SSLSocketImpl.startHandshake（ SSLSocketImpl.java:1375）com.sun.mail.util.SocketFetcher.configureSSLSocket（SocketFetcher.java:549）com.sun.mail.util.SocketFetcher.createSocket（SocketFetcher.java:354）com.sun.mail .util.SocketFetcher.getSocket（SocketFetcher.java:211）at com.sun.mail.smtp.SMTPTransport.openServer（SMTPTransport.java:1927）... 5更多引起：sun.security.validator.Valid atorException：PKIX路径构建失败：sun.security.provider.certpath.SunCertPathBuilderException：无法在sun.security.validator上的sun.security.validator.PKIXValidator.doBuild（PKIXValidator.java:387）找到所请求目标的有效证书路径 . 位于sun.security.ssl.X509TrustManagerImpl.validate（X509TrustManagerImpl.java:324）sun.security.ssl的sun.security.validator.Validator.validate（Validator.java:260）的PKIXValidator.engineValidate（PKIXValidator.java:292） .X509TrustManagerImpl.checkTrusted（X509TrustManagerImpl.java:229）at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted（X509TrustManagerImpl.java:124）at sun.security.ssl.ClientHandshaker.serverCertificate（ClientHandshaker.java:1460）... 16更多引起：sun.security.provider.certpath.SunCertPathBuilderException：无法在sun.security.provider.certpath的sun.security.provider.certpath.SunCertPathBuilder.build（SunCertPathBuilder.java:145）找到所请求目标的有效证书路径 . SunCertPathBuilde r.engineBuild（SunCertPathBuilder.java:131）at java.security.cert.CertPathBuilder.build（CertPathBuilder.java:280）at sun.security.validator.PKIXValidator.doBuild（PKIXValidator.java:382）... 22更多

有人能帮我吗？ :(