code: def _get_addresses(self, address_data, retain_name=False):
          
          if retain_name:
              raise NotImplementedError(
                  "Not yet implemented, but will need client-code changes too"
              )
  
          # We trust than an email address contains an "@" after
          # email.utils.getaddresses has done the hard work. If we wanted
          # to we could use a regex to check for greater email validity
  
          # NB: getaddresses expects a list, so ensure we feed it appropriately
          if isinstance(address_data, str):
              if "[" not in address_data:
                  # Definitely turn these into a list
                  # NB: this is pretty assumptive, but still prob OK
                  address_data = [address_data]
  
          output = [x[1] for x in getaddresses(address_data) if "@" in x[1]]
          return output
docs: Takes RFC-compliant email addresses in both terse (email only)
          and verbose (name + email) forms and returns a list of
          email address strings
  
          (TODO: breaking change that returns a tuple of (name, email) per string)