In 1984 a letter to the White House, addressed to Ronald Reagan was answered with a formal thank you note and letter from the White House itself (documented in an interview in Rubberstamp madness issue in 1985 by Kate Lanxner, I've documented it somewhere on the Internet too....
Hi Lesley! You also got formal acknosledgement from the UK's Prime Minister if you send something to 10 Downing Street. Most Government Departments will give you a formal acknowledgement of mail received.
I wonder if Cameron is any good at mail art?? One day I'll give him a try and see what he comes up with.
If you are thinking of 'cold-mailing' the good and the graet, you could send them some very early Xmas cards, and see if they add you to their list and send you something back in a few weeks time.
I suspect that you might be wasting your time, money, card and glue, though.
Alternatively, you could mail ME something.
I've come across a couple of books in the UK in which people have had 'frivolous' correspondances with the Great and the Good. One was by a guy who lived in the South of England and decided that he didn't want to be in the European Union. So he wrote to everyone (the Prime Minister, lots of British Government Departments, the Queen, the Pope, the US President, the World Bank, the UN, etc) saying that his house ('14 Victoria St', or something) was leaving the EU on a certain date, starting its own currency, issuing its own passport, etc.
He got some incredible replies, and 99% of the people he wrote to (including the UK Ambassador to Washington, who I got to know as an External Director of the company I used to work for) took him seriously. The letters he sent and received formed his book.
Now, what I suggest is that you write to Famous Addresses (however you define them) proposing some sort of International/Global/Universal Mail Art Exhibition to be held in, say, 2 years time (or corresponding to some sort of famous anniversary) and asking if they would like to be associated with it, and/or be an institutional sponsor, and/or publicise it on their web-site, and/or nominate a member to the Advisory Board,and/or host it for a while as it tours the world, and/or anything you like really.
What you send and what you receive in reply could be shared with us.
And if it ever really gets off the ground, remember who suggested it to you in the first place: moi!