Java mail message reading exception when sending a mail through java 6 with port 465 - jakarta-mail

Question

Hi I am sending an email through java application.
When I am running the code through java 7, mails sends properly.
But when I am running the code through java 6, I got following exception
javax.mail.MessagingException: Exception reading response;
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.readServerResponse(SMTPTransport.java:1611)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1369)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:412)
at javax.mail.Service.connect(Service.java:310)
at javax.mail.Service.connect(Service.java:169)
at javax.mail.Service.connect(Service.java:118)
at javax.mail.Transport.send0(Transport.java:188)
at javax.mail.Transport.send(Transport.java:118)
at com.demo.MySendMails.sendMail(MySendMails.java:477)
at com.demo.MySendMails.BirthDayMail(MySendMails.java:291)
at com.demo.MySendMails.main(MySendMails.java:535)
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 com.sun.net.ssl.internal.ssl.Alerts.getSSLException(Alerts.java:174)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1731)
at com.sun.net.ssl.internal.ssl.Handshaker.fatalSE(Handshaker.java:241)
at com.sun.net.ssl.internal.ssl.Handshaker.fatalSE(Handshaker.java:235)
at com.sun.net.ssl.internal.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1206)
at com.sun.net.ssl.internal.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:136)
at com.sun.net.ssl.internal.ssl.Handshaker.processLoop(Handshaker.java:593)
at com.sun.net.ssl.internal.ssl.Handshaker.process_record(Handshaker.java:529)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:925)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1170)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readDataRecord(SSLSocketImpl.java:785)
at com.sun.net.ssl.internal.ssl.AppInputStream.read(AppInputStream.java:75)
at com.sun.mail.util.TraceInputStream.read(TraceInputStream.java:110)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
at com.sun.mail.util.LineInputStream.readLine(LineInputStream.java:88)
at com.sun.mail.smtp.SMTPTransport.readServerResponse(SMTPTransport.java:1589)
... 10 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:323)
at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:217)
at sun.security.validator.Validator.validate(Validator.java:218)
at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:126)
at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:209)
at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:249)
at com.sun.net.ssl.internal.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1185)
... 22 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:174)
at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:238)
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:318)
... 28 more
Here I am using gmail as my mail server and i am using following propertie
Properties props = new Properties();
props.put("mail.smtp.port","465");
props.put("mail.smtp.host","smtp.gmail.com");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory"); //SSL Factory class
I am not shore because of using 465 port do I need to enable SSL and key value should be smtps instead smtp, in email properties?
Is there any certification to be enabled in java 6 for sending a mail using smtp protocall.
If any such guide me in resolving the above issue