Set the property "mail.pop3.socketFactory.fallback" as false and see. By default this property is set as true and it tries to create a socket using the java.net.Socket when it fails to create a socket using the specified socket factory.
http://java.sun.com/products/javamail/javadocs/com/sun/mail/pop3/package-summary.html sample code:
Properties props = System.getProperties();
props.setProperty("mail.pop3.socketFactory.fallback", "false");
Session session = Session.getInstance(props, null);
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