docs: public final static boolean isMailAddress(String str)
      {
          int atIndex = str.indexOf('@');
          if ( atIndex == -1 ) {
              return false;
          }
          
          if ( ! StringUtil.isLetterOrNumeric(str, 0, atIndex) ) {
              return false;
          }
          
          int ptIndex, ptStart = atIndex + 1;
          while ( (ptIndex = str.indexOf('.', ptStart)) > 0 ) {
              if ( ptIndex == ptStart ) {
                  return false;
              }
              
              if ( ! StringUtil.isLetterOrNumeric(str, ptStart, ptIndex) ) {
                  return false;
              }
              
              ptStart = ptIndex + 1;
          }
          
          if ( ptStart < str.length() 
                  && ! StringUtil.isLetterOrNumeric(str, ptStart, str.length()) ) {
              return false;
          }
          
          return true;
      }