Not long ago you could buy special air-mail letters. These were thin blue paper, with an envelope front printed on one side and a gummed trip on the other. You&#x27;d write your letter on the back, fold them up and stick them down, and post at reduced rates (because they were guaranteed to be light, having no enclosures).<p>I haven&#x27;t seen one for ages. I hope they haven&#x27;t vanished completely; they were a really good idea...