Most big companies started retaining email indefinitely after the Monica Lewinsky scandal, and then started automatically deleting it after the Sony hack. I wou

Most big companies started retaining email indefinitely after the Monica Lewinsky scandal, and then started automatically deleting it after the Sony hack. I would expect the balance of whether to retain or delete email to continue to change every decade or so based on what's the least cheapest given the current security threat landscape and legal situation. (The exception being financial firms and other companies in highly regulated industries, which are still required to retain all communication.)