Imagine this scenario:
You are working for a company in a particular role. You leave the company after a certain period of time. Two things happen. You obviously lose your email account, and all the emails associated with it (unless, of course, you keep a copy of everything). And, the company loses all the email (information) that was in your possession. Technically, the company doesn't lose your email communications, but it no longer uses it. Unless, to answer a court subpoena.
What organizations need to realize is that there is a lot of information in these communications. They need to mine the emails and get the most out of them.
Individuals need to realize that all email communications over the company email network should strictly be work related. There are plenty of places where you can conduct your personal conversations. It irks me when I see people complaining that they lost all their emails when they left their employer.
There is a solution to all this.
Every employee working for a corporation is playing a role. Every employee has certain roles and responsibilities in the organization. When one employee moves to another role/organization, most often, another employee takes that role.
Email accounts should be based on roles and people playing those roles. Once someone playing a particular role moves on, the next person taking the role will inherit all email communications pertaining to the role. Any and all email communication done over a corporate network belongs to the company. So, stop whining that the company is passing 'Your' emails to another person. Those emails pertain to the role, and you were playing that role. Role based emails keep the data alive, and useful to corporations.
What this means is that all employees need to keep their personal emails completely separate, which is what most of us are doing anyway. And, corporations need to set up proxies to mimic the way email works today: make it seem personal.