I think it would add a layer of fun to have every primary residence have a free mailbox, that defaults to bring by the door. It would be a small mostly one-way bin for people to send you stuff. (maybe you could take something out if you put it in there, but otherwise it would be to send stuff to the homeowner)
1. It would give people a reason/excuse to visit each others homes more often because it would bypass the mail fee. (Not a big cost, but, ya know)
2. It would make homes feel more useful in the early game.
3. The mail box could get larger for larger homes.
I don't think it should take up available slots in houses. If we want people to visit each others hones more to get more of a sense of community.
Just an idea. To me it would make homes feel more, homey? What does everyone one else think?