Reduce unnecessary encoding work

			raise RuntimeError(

				"Session.extension() may only be awaited before the HEADERS phase",

			)

		bname = name.encode("utf-8")

		while self.phase <= Phase.ENVELOPE:

			message = await self._broadcast.receive()

			match message:

				case Unknown():

					bname = name.encode("utf-8")

					if message.content[:len(bname)] == bname:

						return message.content

				# fake buffers for MAIL and RCPT commands