Q: "sun.security.validator.ValidatorException: No trusted certificate found" error message when connecting gmail

A: The error is due to Java not trusting the certificate from GMail. Newer version of JVM solve the problem. Ruben Suarez provides a solution for those cannot upgrade:

To solve the problem you must add gmail server certificate to the default cacerts keystore of the jre.

To do that follow these:

• Get gmail server certificate (you can simply do this opening https://gmail.google.com in Internet Explorer, press status bar padlock icon to open certificate, go to Details and Copy into file... and selct X.509 binary DER) and save it as gmail.cert
• Execute command similar to this: keytool -keystore

C:/j2sdk1.4.2_01/jre/lib /security/cacerts -import -file C:/g4j-0.3.10/gmail.cer -alias gmail

• NOTE: When asked type "changeit" as this is the default cacerts password
  Restart GMailer4J

That's it. Now your can login to your account ^_^

Thanks Ruben!