Block Mailbox tagging?

The question highlights a deficiency in the tagging of post boxes / letterboxes that should be "addressed" (pun not intended!).

There does not appear to be a tag for a mail box used for inbound mail. In Australia we refer to such things (outside houses and groups of apartments) as "letterboxes" - they are small privately-owned boxes for inbound mail - located on private land, usually just off the sidewalk. Here, the postal service never collects mail from letter boxes.

The wiki assumes an amenity=post_box is a larger box provided by the postal service (often placed on public land such as a sidewalk), where a community deposits outbound mail.

In the absence of tagging for a residential "letterbox" function (or more accurately, a combined postbox/letterbox in your case), I'd consider adding some custom tags to post_box like... amenity=post_box type=residential (or private) inbound=yes outbound=yes

You could also add the street address to the node... and there might be a way to add the range of unit / apartment / flat / lot numbers that are serviced by the group of letterboxes. The address tags for building entrance nodes cater for ranges of apartment (flat) numbers, so perhaps a similar adoption in this case is appropriate.

Canada as an established tagging scheme for those. Until it, these use the normal amenity=post_box (because the Canadian ones, at least allow mail to be posted there, though smaller than at the traditional boxes), with the type=cmb identifying them. Here's one.