I was working there when this happened, and I definitely remember thinking, "Well, no point in writing a detailed email full of information that will be useful in the future, because in 30 days it'll be gone anyway."

Even more frustrating was finding myself in a situation where I remembered an old email that would be enormously helpful, either because of the information in it, or because I could reuse the bulk of something I had invested a lot of effort into writing, and knowing that this work was gone forever.