createHTML = function (string, tag, attribute, value) {
  var S = String(defined(string));
  var p1 = '<' + tag;
  if (attribute !== '') p1 += ' ' + attribute + '="' + String(value).replace(quot, '&quot;') + '"';
  return p1 + '>' + S + '</' + tag + '>';
}
returns the sender's address
@return {Buffer}