I think "inbox" is a no brainer. Everyone understands what it means.
Outbox is not as easy because email clients never made "outbox" a real thing. For that, I do think "Home" could be a better name because it suggests that this is the relay that has your posts for others to see, your home on the web. And you should be very careful on the relays you select to be your home. "Getting posts from people's outbox" is a weird thing to say. And "Getting posts from people's home relays" is better understood.
FYI,
1. I use kind 10013 to your "unpublished write" relays, which I call Private Home as described in the Generic Draft NIP: github.com/nostr-protocol/nips/pull/1124
2. Your private inbox to me is not an inbox. It's either an index relay (like purplepag.es) or a new kind that could lists large relays on the hopes of finding events the client can't find anywhere else.