code: def addr_spec(self):
          
          nameset = set(self.username)
          if len(nameset) > len(nameset-parser.DOT_ATOM_ENDS):
              lp = parser.quote_string(self.username)
          else:
              lp = self.username
          if self.domain:
              return lp + '@' + self.domain
          if not lp:
              return '<>'
          return lp
docs: The addr_spec (username@domain) portion of the address, quoted
          according to RFC 5322 rules, but with no Content Transfer Encoding.