"couldn't reach the mailbox" message

Personally I think it's can be a pathing issue or the game failing to generate the postman. Even though I have a mailbox that requires him to climb four stories of stairs my mailman will still appear, climb up it, and deliver my mail, but some days he doesn't bother with the exercise and I get that message.

I think its quite random. One day they deliver the mail just fine, the next I get that message. My current mail box has been in the same place at least 2 sim-years. Not been moved, nothing has been placed near it. I think they are just feeling lazy that day, and won't bother to walk all the way across the 'hood.

If you play Windenburg and end up with the one small house up on a hill not far from a bar (the one with the winding dead end road), that is a pretty isolated area and it can take a lot longer to get your mail, even without anything in the way, the mail carrier doesn't show up at all despite saying they got the mail to your box.

The game obviously has something in place if the sim can't get to that mailbox, regardless it all done by teleporting the mail to the box.