Just a couple of years ago, most corporate legal counsels viewed electronic records (especially email) as a huge liability. Many CEOs assume that there is some problematic content on their systems. Consequently, many companies implemented 30-, 60- or 90-day deletion policies -- as an email on the server ages-out, it is deleted. In that way, corporate legal counsels and CEOs and CIOs thought they were reducing their liability by eradicating potential "smoking guns" from the email server.
Over the last few years, many corporate legal counsels have started to recognize that you cannot guarantee that emails are deleted. And in many cases, one email that really looks bad can often be mitigated when viewed in the context of the entire message thread. Today, many counsels would rather keep all emails and have the complete thread versus having an outside counsel find one really bad email taken out of context. Keeping email for longer periods of time (if you have the storage resources) is probably going to lessen liability rather than increase it.