Cuneiform tablets have kept information safe across millenia, but hard drives have lifespans of just a few years. Even if your CDs survive the century, their players might have become obsolete, warns the Boston Globe. "Who knows how long they're going to last—how much time before the information on a zip disk just goes into cyberspace heaven," said one archivist.
With digital information storage beset by the ravages of time on one side and format changes on the other, how can you be sure your old emails are safe? If you don't want to print them out, the best bet may be continually updating their file formats. People are already using such rescue techniques on their old 45s and cassette tapes.