In Ireland we were very late to the postcode game and when we introduced them a few years back they actually uniquely identifies a single address. We also continued our "interesting" habit of renaming everything to make them sound more Irish so they are called Eircodes. In theory you could just put the single 7 character Eircode on a letter and it would be enough although our postal service has said we can't do that.
lblume|1 month ago
Macha|1 month ago
Now asking An Post to overhaul their system to work on postcodes only is a bit like asking a postal service which requires postcodes to make them optional. It's technically possible, sure, but they're not going to want to spend the money.
_That said_, An Post's last resort routing department is pretty famous for getting the right address from pretty fragmentary information like "Mary down by the church, formerly of Kilnowhere", so I'm sure if a letter with just a eircode arrived there they'd sort it, but I imagine that An Post don't want to encourage people doing things that increases load on the labour intensive sorting.