code: async def ehlo(
          self, hostname: str = None, timeout: DefaultNumType = _default
      ) -> SMTPResponse:
          
          if hostname is None:
              hostname = self.source_address
  
          async with self._command_lock:
              response = await self.execute_command(
                  b"EHLO", hostname.encode("ascii"), timeout=timeout
              )
          self.last_ehlo_response = response
  
          if response.code != SMTPStatus.completed:
              raise SMTPHeloError(response.code, response.message)
  
          return response
docs: Send the SMTP EHLO command.
          Hostname to send for this command defaults to the FQDN of the local
          host.
  
          :raises SMTPHeloError: on unexpected server response code