It's my understanding, and I could be wrong, that you put notes in your Outbox relays. But when you reply to someone's note, it makes sense to also send those replies to the mentioned users' Inbox relays. And when you want a user's notes, you get them from that user's Outbox relays.

I think that's what Amethyst does now. And now I'm all thought up in knots, and I'm going to take a break.