Any postal address can be used to receive postcards and letters. Just identify one or more decision makers in government, business, local services, etc. Then ask your supporters to send a postcard or letter and it will be printed and posted.
Like politicians, other decision makers take printed post seriously and usually respond.
PostBug actions can be sent to government ministers, corporations and government company CEOs and board members, newspaper editors, media outlets and more. They can even be sent to a supporter's neighbours, family, friends and colleagues if they supply the address. The recipient is up to you based on your goals and strategy.
Power is never only wielded by the obvious front-people: heads of governments and companies. A whole host of other people are highly influential behind-the-scenes. These behind-the-scenes people often don't have sophisticated defences like assistants, PR teams, media training, etc.
So senting postcards and letters to these people can have a double effect:
So don't just go for the obvious recipients, considering the "power behind the throne".