> An Post, don't use the postal code as their primary way to direct mail (as far as I understand) .

I'm not sure how the delivery system works exactly, but I think they use the eircode? Especially in the countryside there often isn't much more than that. At my previous address the street doesn't even have a name; but post addressed to "my name, town, eircode" got delivered.

Also when the eircode was first introduced it really messed up the delivery, which seems to indicate they're using it?