code: public void simplify()
    {
      // remove all addresses from the cc and bcc that are in the to address set.
      ccSet.removeAll(toSet);
      bccSet.removeAll(toSet);
  
      // remove all address from the bcc set that are in the cc set.
      bccSet.removeAll(ccSet);
    }
docs: Simplifies this email by removing duplicate pieces of information.  The standard implementation removes duplicate
  recipient emails in the to, cc, and bcc sets.