Przeszukałem kilka pokrewnych postów tutaj i w innych miejscach, ale żaden z nich nie rozwiązał mojego problemu. Mam program, który wysyła e-maile do zestawu osób korzystających z „javamail API”. Raz działało dobrze. Dzisiaj potrzebowałem ponownie, ale nie mogę wysłać żadnej wiadomości e-mail ... Moja metoda sendEmail jest następująca:

public void sendEmail(String userName, String password, String toAddress, 
       String subject, String message, String[] attachFiles) 
       throws AddressException, MessagingException {

     // sets SMTP properties
    Properties properties = new Properties();
    properties.put("mail.smtp.host", "smtp.gmail.com");
    properties.put("mail.smtp.port", "587");
    properties.put("mail.smtp.auth", "true");
    properties.put("mail.smtp.starttls.enable", "true");
    properties.put("mail.user", userName);
    properties.put("mail.password", password);

    // creates a new session with an authenticator
    Authenticator auth = new SMTPAuthenticator(userName, password);
    Session session = Session.getInstance(properties, auth);

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

    try {
        msg.setFrom(new InternetAddress(userName, "My name"));
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    }
    InternetAddress[] toAddresses = {new InternetAddress(toAddress)};        
    msg.setRecipients(Message.RecipientType.TO, toAddresses);
    msg.setSubject(subject);
    msg.setSentDate(new Date());

    // creates message part
    MimeBodyPart messageBodyPart = new MimeBodyPart();
    messageBodyPart.setContent(message, "text/html");

    // creates multi-part
    Multipart multipart = new MimeMultipart();
    multipart.addBodyPart(messageBodyPart);       

    // adds attachments
    if (attachFiles != null && attachFiles.length > 0) {
        for (String filePath : attachFiles) {
            addAttachment(multipart, filePath);
        }
    }

    // sets the multi-part as e-mail's content
    msg.setContent(multipart);

    // sends the e-mail
    Transport.send(msg);

}

Tak więc teraz próba wywołania tej metody otrzymałem następujący błąd (używam jdk 1.7.0_21):

Sending email Failed...

javax.mail.MessagingException: Could not convert socket to TLS;
  nested exception is:
    javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at com.sun.mail.smtp.SMTPTransport.startTLS(SMTPTransport.java:1907)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:666)
    at javax.mail.Service.connect(Service.java:367)
    at javax.mail.Service.connect(Service.java:226)
    at javax.mail.Service.connect(Service.java:175)
    at javax.mail.Transport.send0(Transport.java:253)
    at javax.mail.Transport.send(Transport.java:124)
    at EmailSender.sendEmail(EmailSender.java:86)
    at CFP_LaWasp_EmailSender.sendCFPLaWasp(CFP_LaWasp_EmailSender.java:178)
    at CFP_LaWasp_EmailSender.main(CFP_LaWasp_EmailSender.java:220)
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
    at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1886)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:276)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:270)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1341)
    at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:153)
    at sun.security.ssl.Handshaker.processLoop(Handshaker.java:868)
    at sun.security.ssl.Handshaker.process_record(Handshaker.java:804)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1016)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1312)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1339)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1323)
    at com.sun.mail.util.SocketFetcher.configureSSLSocket(SocketFetcher.java:528)
    at com.sun.mail.util.SocketFetcher.startTLS(SocketFetcher.java:465)
    at com.sun.mail.smtp.SMTPTransport.startTLS(SMTPTransport.java:1902)
    ... 9 more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:385)
    at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
    at sun.security.validator.Validator.validate(Validator.java:260)
    at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:326)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:231)
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:126)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1323)
    ... 19 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:196)
    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:268)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:380)
    ... 25 more

Nie wiem, jak rozwiązać ten problem, ponieważ wcześniej działał ... Nie wiem też, czy mój Gmail ma z tym coś wspólnego (jeśli zablokował ten dostęp ...)

Doceniam każdą pomoc.