Other's inbox relay are transparent from user's point of view, who should not have to worry about it.

I think that the main source of confusion is related to the fact the 99% of the time two different relays, inbox and outbox, are not really needed, they can be a single personal public relay.

Clients should just allow to add them, and only in an advanced configuration let the user tweak the read/write permissions (or deduce them by the actual permissions).

Then the user can be allowed to add an optional DM relay (suggesting that it enforces authentication), a search relay, etc.

As you see users think that the relay setting in Amethyst is quite confusing, after the Outbox model update; this approach could solve this.