Java class to validate email addresses

We have an application which stores email addresses, built using Java. All we've come up with is a regular-expression checker whether an email address is VALID (i.e. the formatting is okay...). We want to actually VALIDATE whether the email address being entered is DELIVERABLE (that the mailbox exists and can receive messages). Your task is simple - create a pure java class that has one method: public boolean isEmailDeliverable(String emailAddress) { }