javax.mail.MessagingException: PKIX path building failed: SunCertPathBuilderException: unable to find valid certification path to requested target;

I get this Exception when I try to connect to the store.

As I look through forums, the solution to this error is to add the certificate to the truststore file of the used JVM.

The problem is I am new to this and I am not sure that I understand how I should do this exactly: Where should I get the certificate and how should I add it?

N.B: I notice that when I run this using main method, it works fine! But when I set a Scheduler to call the method automatically, that's when I get the exception.

Thank you a lot for the help.

public void receiveMails() throws Exception
    {

        Properties props = new Properties();
        props.setProperty("mail.store.protocol", "imaps");
        props.setProperty("mail.imaps.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.setProperty("mail.imaps.socketFactory.fallback", "false");
        props.setProperty("mail.imaps.ssl.enable", "false");
        props.setProperty("mail.imaps.socketFactory.port", "993");
        props.setProperty("mail.imaps.starttls.enable", "true");
        props.setProperty("mail.imaps.ssl.trust", "mailHost");

        try
        {
            
            Session session = Session.getInstance(props, null);
            Store store = session.getStore();
            store.connect("mailHost", "user@domain.com", "password");
//...

The Exception is:

javax.mail.MessagingException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target;
  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.imap.IMAPStore.protocolConnect(IMAPStore.java:479)
	at javax.mail.Service.connect(Service.java:275)
	at javax.mail.Service.connect(Service.java:156)
	

Try disabling your antivirus while doing this operation. This might be the cause.