We own 2 houses, one of which is used as storage for our garden machinery. We have owned this property for about 8 years, but we still get mail delivered there for the previous owners.

In England, I would simply write across the envelope " no longer at this address" or something similar, and drop it in a post box.

Does the same principal work in Hungary?

I think here in Hungary they are very slow to update address changes. My Hungarian bank account keeps displaying my first address when I moved here five years ago! Luckily our Magyar Posta lady knows and delivers any incorrectly addressed letters to our house.