Adjustable height mailbox

[dwdanby]

I'm moving soon to a small town where they keep changing the required height of the mailboxes, based on changes in delivery vehicles. I want to both solve the problem and have a bit of fun. I want to create a mailbox mount that can be adjusted up and down. I thought of either a) part of a bike frame with the mailbox attached to the seatpost or b) some sort of telescoping mount like a tripod, or a TV wall mount. The result has to be very sturdy so the mailbox doesn't move around when opened, which is making me lean toward the bike frame / seat post idea. Could I get some input? Thanks all!