protected void writeMailbox(int which, int what, int answer)
			throws Exception {
		if (which < 0 || which > 9) {
			return;
		}
		writeStream(String.valueOf(which));
		writeStream(String.valueOf(what + 1));
		if (debug) {
			System.out.println(name + "(d): send " + what + " on " + which);
		}
		if (!readStream().equals("success")) {
			throw new Exception();
		}
		if (answer >= 0 && answer <= 9) {
			readMailbox(answer, true, -1);
		}
	}