Hi Paul
Outgoing: there is no problem. The post box on site is taken to the post office nearly every day. The post office in town is the best place to get stamps and post mail from. At least that way you pay the correct postage 'size does matter'!!!
Incoming: Can be problematical. It
MUST have your buzon number on it or it gets returned to sender (even if the rest of the address is correct). We've had post go astray even when the sender assures us that the buzon has been used. It may be that the 'postie' puts it into the wrong box - belonging to an unbuilt property or holiday home, they may appear sometime! Oversized/registered packages are not delivered, you get a note to collect from the post office.